Doctoral Thesis

Analytical Methods for Low-Voltage Meshed Network Challenges

Final Thesis 4.96 MB Summary of Thesis 4.96 MB

Author of thesis: Ing. Vít Krčál, Ph.D.

Acad. year: 2025/2026

Supervisor: doc. Ing. David Topolánek, Ph.D.

Reviewers: prof. Ing. Peter Braciník, Ph.D., prof. Matti Lehtonen

Abstract:

The thesis focuses on meshed distribution networks, which pose distinct operational challenges in analysis, optimization, protection, and diagnostics. The work is motivated by the lack of state-of-the-art research on meshed topologies and by practical needs expressed by a cooperating distribution system operator. A representative numerical model of an urban low-voltage meshed network is developed as the basis for simulations, case studies, and the design of new methods. The thesis addresses four main areas concerning fault scenarios: short circuits in the meshed network, faults in the upstream network, feeder outages with cascading failures, and interruptions of low-voltage fuses. A new methodology for calculating peak short-circuit currents is introduced, incorporating the current-limiting effect of fuses, and optimization methods for network reconfiguration are compared with the aim of minimizing excessive fault current levels. Upstream active power flow protection is analyzed, with a procedure proposed for deriving selective protection settings based on simulated medium-voltage fault scenarios. Simulations of multiple medium-voltage feeders’ outages are conducted to assess the network resilience and identify the weakest elements in the network, pointing out the danger of cascading failures. Furthermore, a threshold-based method for detecting low-voltage fuse interruptions was designed and tested, based on distributed measurement system monitoring current changes in low-voltage feeders. The presented research delivers a unique European-style meshed test network model and novel approaches tailored to this topology, aiming to advance secure and efficient operation. The thesis contributes both methodological advances and practical tools applicable for distribution system operators, while also opening directions for future research on optimization and diagnostics in meshed distribution networks.

Keywords:

Meshed distribution network, short-circuit, optimization, resilience analysis, cascading failure, fault indication, upstream active power flow, fault analysis, distributed measurement system

Date of defence

15.12.2025

Result of the defence

Defended (thesis was successfully defended)

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Process of defence

The defence took place in the presence of the committee members. During the defense, the doctoral student presented the results of his dissertation to the committee, including his own contributions. After the doctoral student's presentation, his supervisor informed the attendees about his evaluation of the entire course of study. This was followed by the presentation of the referees' reports and a discussion of the referees' questions and comments. Then, in the public discussion, questions and comments on the dissertation were presented by prof. Drapela, prof. Toman. A written record of the questions is attached to the minutes. All questions raised by the opponents and in the public discussion were correctly addressed by the PhD student. The PhD student has demonstrated creative ability in the given research area, and the thesis meets the standard requirements for a dissertation in the field. In a closed discussion and after a secret ballot, the committee concluded that the doctoral candidate has fulfilled the conditions of Section 47, Paragraph 4 of the Higher Education Act No. 111/98 and can therefore be awarded the degree of Doctor (PhD).

Language of thesis

English

Faculty

Fakulta elektrotechniky a komunikačních technologií

Department

Department of Electrical Power Engineering

Study programme

Power Systems and Power Electronics (DKC-SEE)

Composition of Committee

prof. RNDr. Vladimír Aubrecht, CSc. (předseda)
doc. Ing. Ondřej Vítek, Ph.D. (člen)
doc. Ing. Jan Bárta, Ph.D. (člen)
prof. Ing. Petr Toman, Ph.D. (člen)
doc. Ing. Jaroslava Orságová, Ph.D. (člen)
Ing. Petr Modlitba, CSc. (člen)
prof. Ing. Jiří Drápela, Ph.D. (člen)
prof. Ing. Peter Braciník, Ph.D. (člen)
prof. Matti Lehtonen (člen)

Supervisor’s report
doc. Ing. David Topolánek, Ph.D.

Vít Krčál began his PhD studies in 2019. He passed the doctoral state examination in 2021 and submitted his dissertation in October 2025.

The dissertation focuses on the operation of low-voltage mesh networks, which are primarily used in large urban distribution systems. Due to their specific configuration, characterised by high meshing, they differ significantly from conventional low-voltage systems and thus present numerous challenges that have not been extensively resolved within current scientific and research knowledge. This was also the reason for the relatively large thematic scope of the work, which addresses a few prioritised areas: issues of high short-circuit current levels, indication of cascading faults, indication of damaged fuse or line interruptions, and settings for active power overflow protection to achieve selective tripping of high-voltage faults. The selection of these areas was made based on demands from distribution system operators and also overlaps with the applied research projects that were being addressed.

During his studies, Vít Krčál invested significant effort in developing the dissertation's theoretical and practical components, demonstrating independent scientific capability.

As part of his studies, he contributed to teaching exercises in Distribution and Industrial Networks and participated in eight applied research projects funded by the Czech Technology Agency (TAČR), resulting in eight outputs co-authored by Vít Krčál.

In the academic year 2021/2022, he spent three months at Aalto University in Finland.

Vít Krčál is the author or co-author of 15 international conference papers, 6 national conference papers and 3 articles in an impact-factor journal. There are 15 records in the Scopus database and 2 records in the Web of Science database; his h-index is 1.

The candidate meets all prerequisites for the Doctor title. I recommend the dissertation for defence.

Reviewer’s report
prof. Ing. Peter Braciník, Ph.D.

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Posudek oponenta [.pdf] 177,14 kB

Reviewer’s report
prof. Matti Lehtonen

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Posudek oponenta [.pdf] 817,21 kB

Responsibility: Mgr. et Mgr. Hana Odstrčilová