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PhD theses in progress

Daniel Fank: Damping of Inter-Area Oscillations with Combined Control Strategies at Hydro Power Plants
Inter-area oscillations can endanger the stability of the power grid system and damping of such oscillations, is one of the major concerns for the power system operators. These oscillations are caused by switching operations or by a failure of transmission lines. Inter-area oscillations are a problem, because they reduce the limits of power transfer capacity and they can occur power line disconnections, with the worst-case scenario of a blackout at the power system. The continuous reduction of conventional power plants makes it mandatory to provide additional damping capacity in the power system. In this thesis, the potentials of combined control strategies at hydro power plants are investigated to improve the damping behavior of inter-area oscillations and the robustness of the power system.

Benjamin Jauk: Soil model optimization for earthing system design regarding personal safety
This PhD thesis aims to continue the work of the master’s thesis that highlighted the fact that fundamental research in this field is critically needed and it is envisioned to fill the gap by introducing inverse modelling to earthing systems design. A better understanding of changing soil parameters, and soil measurements will be developed to ensure the modelling of a sufficiently accurate soil model that can ensure personal safety. The modelling will be carried out so that a general statement can be made about the effects of the soil on earthing systems and the influence on personal safety. In addition, an impact assessment of various parameters will be carried out for the obtained soil resistivity distribution.
Based on this fundamental research, yielding a verified inhomogenous model of the soil, the impedance to earth can be synthesized, which is a main factor for personal safety.

Martin Fürnschuß: Analysis and Modelling of Earthing and Equipotential Bonding Systems in Electrical Power Systems.
Earthing and equipotential bonding and lightning protection systems (EEBLPS) are still an essential part of protective measures. In addition to the classical protective measures such as protection of persons, animals and goods, modern EEBLPS should also make a valuable contribution to EMC (electromagnetic compatibility) both in the low-frequency range and in the transient range, as in the case of switching operations and short-circuits. In the dissertation, three-dimensional meshed EEBLPS are modelled, these are integrated into existing EEBLPS or infrastructure and vagabond currents and voltage distortions in the low-frequency as well as in the higher-frequency range are calculated. On the basis of the current distribution in the EEBLPS, statements can be made with regard to the influence of interference on exemplary existing information and communication technology facilities and subsequently improvement measures of the EEBLPS can be taken, e.g. through suitable meshing, cable routing or cable shielding handling.

Markus Resch: Holistic analysis and verification of the use of large-scale Battery Energy Storage Systems in a rural medium voltage distribution grid
In terms of the optimal operation of a distribution grid, requirements for the use of battery storage arise, which on the one hand aim at increasing the quality and security of supply, while at the same time relieving the distribution grid infrastructure, but also at minimizing grid losses. These requirements are of particular relevance if the generation and use of energy from renewable resources within the supply area becomes the focus of attention. Based on the technically available possibilities, this results in operating modes of the storage system that require not only an economic but also an ecological consideration, whereby the relationship between the motivations mentioned should be in balance in order to be considered feasible.
These operating modes of the battery energy storage system are to be tested, analyzed and validated in real network applications on the basis of simulation-supported considerations.

Marlene Petz: Advanced Modelling of Resource Adequacy in Austria
In order to ensure security of supply for a country, various tasks need to be performed at the transmission system operator’s sites. One of the key tasks is the assessment of future levels of supply through resource adequacy assessments. The processes and the indicators used to benchmark those levels were introduced in the recent years. Overall, those processes need to be performed at a European level, meaning that all countries participate to the European Resource Adequacy Assessment (ERAA). Basis for those calculations are simplified market models, where for each country the relative constellation of generation units is accounted for a specific target year. In order to reflect stochastic uncertainty resulting from volatile renewable generation and to take into account the temperature dependency of demand, Monte Carlo Simulations are applied. Several hundreds of those calculations are executed and the final results are retrieved by statistical analysis.
Since resource adequacy assessments underlie a trade-off between detailed modelling approaches and calculation times needed for several hundreds of market simulations, the Austrian Power Grid AG is of the opinion that the representation of hydro units is not satisfying at this point of time. Within this thesis, a detailed comparison of different tools and approaches used in the ERAA process is performed with detailed focus on hydro representation. Additionally a new approach to be used in future resource adequacy assessments is presented. Furthermore, a focus will be given to the future development of demand. Additions to the basic load resulting from heat pumps, electronic vehicles, batteries and data centres play an important role. A proper estimate per country of the future development is of outmost importance, as well as the proper representation within the model. Since parts of these load additions can also provide flexibility to the system, the correct representation within the modelling approach will be assessed.
Finally, the potential of Demand Side Response (DSR), available from households and industry will also be added to the system. Resource Adequacy Assessments are important processes placed between politics and technology. In order to fulfil future climate targets, an in-depth cooperation between all involved stakeholders needs to be ensured. In order to properly reflect future development streams guided by policies, I try to help by developing an advanced modelling approach for future adequacy calculations, which comply with all the requirements provided by the clean energy package.

Philipp Hackl: Transient stability investigation of grid forming inverters
The use of renewable energy sources mostly relies on power electronic systems, and the influence of these is already large enough to affect the dynamic characteristics of the power system. Unlike conventional rotating machines, the stability of power electronic systems depends primarily on the applied control strategy. To ensure the reliable operation of power systems in the future, voltage-controlled inverters ("grid forming") may be a possible solution in contrast to the current-controlled inverters ("grid following") used today. Although these new types of control structures have risen in scientific publications in the last few years, there are still some uncertainties about their transient stability and integration in existing grid structures.

Thomas Kern: Performance increase of the Austrian Transmission System for Electricity
The functioning of the western society requires the permanent and sufficient availability of electrical energy. This in turn demands effective and reliable electrical grids. Also in Austria, the backbone of the current electrical power system is the trans-regional and international transmission system – the so called ‘grid level 1’ – all transmission systems above the voltage level of 110 kV.
This dissertation project covers the chronological development of the Austrian transmission system in conjunction with the technological development. Like in all other countries also in Austria the first electrification projects were based on private initiatives, running rather small power stations – often supplying only one costumer with a few applications. Over time, the power stations become larger and got connected amongst each other – integrated grids were formed. A central research issue is if the transmission system in Austria would have realised in the same manner, as it currently exists with today’s knowledge and technology. What was planed and why was it planned in that way? What was planned and finally not realised? Based on the results of the analysis of the past several scenarios and models for possible future developments shall be derived. A technology assessment is also part of this thesis as well as an assessment on possible alternative solutions for the future electrical transmission system of electricity.
Due to the historical part of thesis, it is an interdisciplinary work. Thus the ‘Institute of History’ of the University of Graz is supporting the project.

Hasan Akbari:Variable Speed Hydropower Plants
Hydropower sources are the main part of renewable energy share for electricity generation. They can provide clean and reliable electricity with low greenhouse gas emission in addition to water management possibility. Around 16% of the total electricity production which is 60% of renewable electricity generation is produced by hydropower. In 2019, total installed hydropower capacity reached 1308 GW with the highest generation of 4306 TWh. In Austria, the share of hydropower technology in total electricity generation was around 60% in 2018. Moreover, it is planned to produce up to 85% of total electricity generation by hydropower in Austria in 2030. More importantly, to reach the higher penetration of renewable energy sources in the electricity production, due to uncertainty of wind and photovoltaic systems, there is a vital need to implement a renewable, reliable, accessible, and fast electricity generation sources in the power systems which can be fulfilled by the presence of variable speed pumped storage hydropower plants. Hydropower plants with full-size converter will play an essential role in the future of hydropower generation and also electricity production worldwide. Hydropower plants with full-size converter are very new trend in the area of hydropower industry providing more flexibility and efficiency. With the help of full-size converter, it is possible to operate in variable speed mode and increase the efficiency of turbine/generator unit, in addition, it is attainable to respond faster to some events in the power systems and also it can improve some limitations of conventional synchronous generators. Due to the fact that this technology is quite new, many aspects should be analyzed and considered for reliable and efficient operation of these modern units. Therefore, it is crucial to investigate advantages, challenges, and solutions for hydropower plants with full-size converter in the power systems. One integral research aspect is finding an optimal control strategy for the whole unit (hydraulic part, synchronous generator and full-size converter) to achieve different goals e.g. maximum efficiency, minimum losses, improving stability and reliability. Another important topic is conducting research on the interaction between conventional units (hydraulic system and synchronous generator) and variable speed units (hydraulic system, synchronous generator and full-size converter) in one power plant ore close distance by considering transient and dynamic behavior of hydraulic systems and also possible events in the power systems including short circuit, line trip, and low voltage ride through (LVRT). Moreover, investigation on the start-up and shut-down of variable speed hydro power plants is another valuable research subject.

Philipp Schachinger: Analysis of low frequency neutral point currents and their impact on power grids
Low-frequency neutral point currents superimpose the operating currents in transformers and lead to undesirable effects due to the resulting half-cycle saturation. The effects range from increased transformer noise levels to voltage distortion and blackouts. These low-frequency currents arise in part from the interaction of the earth's magnetic field with solar winds. These geomagnetically induced currents (GIC) are calculated and thereby provide information about critical conditions in the transmission grid.
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Daniel Herbst: A contribution to new approaches in low-voltage protection
Due to the current and expected future developments of electrical consumers (e.g. large-scale roll-out of e-mobility with the necessary high-power charging infrastructure) combined with decentralised generation systems (e.g. volatile renewable energy sources such as photovoltaic systems), new challenges arise for low-voltage grids. In the context of the PhD thesis to be elaborated, these are to be identified on the one hand and possible solutions in terms of additional protective functionalities are to be developed on the other hand. The focus will be on an analysis of the current situation, an enrichment of this with future probable scenarios as well as the development of possible methods and algorithms for tackling them, including their validation. In addition, the effects of the proposed new protection functionalities on the existing conventional low-voltage protection will be evaluated.
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Dennis Albert Investigation of Low Frequency Currents in the Electrical Power Transmission Grid and their Effects on Power Transformers
Low frequency currents (0-1 Hz) (LFC) in the transmission network can have a negative influence on its stability. The currents are caused by geomagnetic influences (increased solar activity, Geomagnetically induced currents, GIC) or other electrical systems, such as direct current powered transportation systems. A main problem caused by the superimposed quasi direct current is the associated saturation of transformers. This increases the reactive power consumption and also the power loss in the transformer.
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