Mahir Muratovic

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Muratovic

First Name

Mahir

ORCID

0000-0003-4563-6267

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Publications1 - 7 of 7

Transmission and Distribution Equipment: Providing Intelligent Maintenance
Franck, Christian; Hsu, Chi-Ching; Xiao, Yu; et al. (2023)
IEEE Power and Energy Magazine
One of the cornerstones of a reliable transmission and distribution grid operation are fully functional components that can operate robustly and with a low outage rate under all specified operating conditions. Dependable maintenance strategies are thus indispensable and are applied by grid operators around the world. One of the present key challenges in most countries with a widely developed transmission and distribution (T&D) grid system are aging components that reach their anticipated end of life. Asset management faces the question if the lifetime of components could be prolonged, and the replacement could be delayed. For this, the health of the components needs to be assessed and is ideally continuously monitored. In addition to this, the currently ongoing transition of the entire energy system leads to a change and increase of the stress to the T&D equipment. The integration of new renewable energy sources on all voltage levels leads to bi‐directional power‐flows and increased variability. The higher demand for electric power not only increases the power flow levels on average, but in particular also the peak flows. The result of this changed and increased stress on the equipment is an accelerated component aging and the need for maintenance strategies to be adopted to this new situation. Recent developments in low‐cost and low‐power data acquisition technology and machine learning based algorithms, combined with rapidly increasing decentralized embedded computing power, offer the opportunity to develop improved and intelligent maintenance strategies based on continuous monitoring and real‐time health evaluation of the equipment. This paradigm changes the prospects in equipment maintenance, offering significantly reduced costs in asset management. The lifetime of properly dimensioned equipment is expected to be several decades, sometimes as much as 40 to 60 years. Most maintenance checks therefore only confirm the excellent condition of the component and would have not been necessary at this point in time. Thus, not only delaying the replacement, but also delaying a maintenance interval based on the health condition would be very welcome. Hence, the most commonly used maintenance concepts are changed from time‐based checks to a new and more intelligent approach, oriented towards a just‐in‐time service. This article aims to introduce the concepts of intelligent maintenance strategies, trends, and challenges of T&D equipment condition monitoring, as well as the automatic estimation of equipment health.
Voltage-Current Characteristic of Free Burning Arcs in SF6 Alternative Gas Mixtures
Pietrzak, Paweł; Engelbrecht, Joseph T.; Simka, Philipp; et al. (2022)
IEEE Transactions on Plasma Science
Voltage-current characteristics of free burning arcs in SF6 and air have been known for decades. As the demand for an SF6-free solution is increasing, there is an accompanying need to determine arc parameters in the alternative gases. An unblown arc experiment has been established to determine the voltagecurrent characteristics of SF6 alternative gases, which have not yet been thoroughly studied. In this experiment free burning arc measurements were performed in a number of gases under consideration of SF6 alternatives, including CO2 and mixtures of CO2 /O2 with and without C4F7N or C5F10O additives at concentrations of up to 10 %. Measurements were also performed in air and SF6 for comparison. Arc voltage was measured in each gas at pressures ranging from 1 bar to 5 bar absolute, and electrode separations ranging from 20mm to 95 mm. Voltagecurrent characteristic measurements for air and SF6 show good agreement with previously published results. A linear relationship of the arc voltage to the arc length is shown, as well as fourth root dependence of the arc voltage on the gas pressure. It was shown that neither the O2 nor the fluorinated additives to CO2 have any significant influence on the voltage-current characteristic. The minimum arc voltage in all measured gases was slightly higher than in SF6, but the arc in SF6 was the least stable and had the highest elongations resulting in high voltage peaks. The arc voltage in air had a similar minimum value to the CO2 based gases, but the arc was much more stable, resulting in lower effective voltage, especially at low currents.
Determination of Discharge Coefficients for Valves of High Voltage Circuit Breakers
Smajkic, Amer; Hadzovic, Belma Bosovic; Muratovic, Mahir; et al. (2020)
IEEE Transactions on Power Delivery
Nowadays, high voltage circuit breaker (CB) simulations are mostly based on Computational Fluid Dynamics (CFD) models. Such simulations require significant computer resources. An alternative approach is to use enthalpy flow models, which do not use space discretization of the interrupter unit chambers and valves. Gas flow is calculated based on state of gas in adjacent chambers and valve settings. However, the valve shape has significant influence on the effective flow cross section between chambers. Therefore, in order to ensure correct simulation results, it is necessary to determine the correct values of discharge coefficients for all valves in the interrupter unit of a circuit breaker. In this paper, the discharge coefficients were determined by combining a series of CFD and enthalpy flow simulations for each valve in the interrupter unit. After that, discharge coefficients are used as input for further simulations based on the enthalpy flow model. This way, benefits from both models are combined: more precise gas flow calculation and faster simulations. The proposed novel approach is validated in a high-power laboratory by pressure measurements on a 420 kV 63 kA self-blast circuit breaker.
Comparative Test Program Framework for Non-SF6 Switching Gases
Franck, Christian; Engelbrecht, Joseph T.; Muratovic, Mahir; et al. (2021)
B&H Electrical Engineering
In recent years, significant achievements have been made with respect to the development of SF6-free gas insulated substations (GIS). In parallel, the interest in installing SF6-free GIS by utilities increased steadily and tenders for new substations or upgrades regularly also include alternative technologies. The excellent performance of SF6 was unequivocally accepted by all vendors and users so that the community became used to single technology solutions. This is no longer the case with alternative gas mixtures, and multiple technological solutions are available. However, from the present body of literature it is not possible to make a full and comparative evaluation of different alternative gas switchgear, i.e. circuit-breakers and disconnectors. Thus, the High-Voltage Laboratory of ETH Zürich started investigations and measurements of basic experiments that allow an unbiased comparison of properties of alternative gas mixtures relevant for switching. The two main purposes of these investigations are to define a set of measurements that allow an estimation and comparison of switching performance with different gas mixtures, independent of a specific interruption nozzle geometry, drive system, electrostatic design, and other design specific features, and to perform (some of) these measurements comparing pure SF6, with air, pure CO2, CO2/O2 mixture, and further specific gas mixtures that are currently proposed by manufacturers for SF6 replacement. The basic analysis behind the definition of measurements will be given in detail and the design principles of the chosen test devices and the derived test currents and diagnostics will be introduced. Test results themselves will not be given, rather they will be the subject of separate future publications.
An Experimental Circuit Breaker for Benchmarking the Intrinsic Interruption Performance of SF6 Alternative Gas Mixtures
Muratovic, Mahir; Engelbrecht, Joseph T.; Simka, Philipp; et al. (2024)
IEEE Transactions on Power Delivery
Currently, there is significant effort worldwide in the research and development of SF6-free high-voltage circuit breakers, both in academia and industry. One of the most important switching capabilities is thermal current interruption, a process that, in modern self-blast breakers, strongly depends on the coupled effects of nozzle geometry, nozzle ablation, back heating, pressure build-up and gas out flow, as well as contact and puffer cylinder motion actuated through the drive. Previously published investigations on the thermal interruption performance of novel switching gases have used such designs, however, due to the many coupled processes, it is not possible to control the interruption conditions in order to make a full and comparative evaluation of different SF6 alternative gas mixtures. The aim of the present contribution is to present an experimental circuit breaker tailored for use in basic experiments that allow for an unbiased comparison of properties of alternative gas mixtures relevant for current interruption. The breaker is based on a novel puffer design with an overpressure relief valve that allows the contact stroke and blow pressure to be predicted, controlled and adjusted over a wide parameter range at current zero. This contribution lists the requirements for such an experimental circuit breaker and focuses on its design realization. Experimental validation is given that this device can be used in benchmarking the interruption characteristics of SF6 alternatives. Systematic comparison of the thermal interruption performance of SF6 alternatives and investigations of the processes around current zero will be reported in other publications.
Vacuum Circuit Breaker Closing Time Key Moments Detection via Vibration Monitoring: A Run-to-Failure Study
Hsu, Chi-Ching; Frusque, Gaëtan; Muratovic, Mahir; et al. (2022)
2022 IEEE International Conference on Systems, Man, and Cybernetics (SMC)
Enhanced Method for Pressure Rise Calculation in SF6 GIS Due to Fault Arcs
Beslija, Dejan; Gorenc, Dalibor; Muratovic, Mahir; et al. (2020)
IEEE Transactions on Power Delivery
Modeling of pressure rise in SF 6 GIS (Gas Insulated Switchgear) due to internal arc faults is a complex and challenging task, due to a large number of highly variable factors, which influence the whole process. This is especially the case in GIS with high rated short circuit currents, where the effects, such as material evaporation and erratic arc behavior, and consequently the pressure build-up rate, are much more pronounced. These severe conditions ultimately determine the design limits and must therefore be carefully investigated. The enhanced internal arc simulation model, presented in this paper, considers the impact of evaporation of different materials on gas properties and the pressure rise, as well as the dependence of released arc energy, thermal transfer and evaporation intensity on the state of gas. The experimental set-up and the test configuration, used to validate the calculation results, are evaluated and discussed. An evident finding, which is supported by measurements, is that the implemented improvements of the basic simulation model (introduced in the Technical Brochure 602 by the CIGRÉ working group A3.24) increase the prediction accuracy of GIS withstand performance during internal arc faults.

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Mahir Muratovic

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