Public defence in Power Systems and High Voltage Engineering, M.Sc. David Sevsek

The title of the thesis: Advanced Earth Fault Mitigation Using Virtual Air Gap Reactors

Doctoral student: David Sevsek
Opponent: Prof. Zdeněk Müller, Czech Technical University, Czech Republic
Custos: Prof. Matti Lehtonen, Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation

Modern electric power systems are undergoing significant changes due to the imminent risks caused by climate change. To reduce greenhouse gas emissions and become more sustainable and resilient, most energy sectors are transitioning from traditional fossil-fuel-based energy sources to electricity as the primary energy source. However, this transition process and the consequences of climate change are putting additional stress on electricity networks, as there is a growing need for reliable and safe electric energy transmission. An example of this need for increased safety is the "Black Saturday" bushfires that occurred in Australia in 2009, where a series of power lines fell to the ground, causing Single-line-to-earth (SLTE) faults, igniting the dry vegetation and resulting in the loss of 173 lives and the destruction of thousands of homes. 

One way to increase the safety and reliability of electricity distribution networks might be by using virtual air gap (VAG) reactors as arc suppression coils (ASCs). These reactors aim to minimize the fault currents that occur during SLTE faults. By reducing the fault currents to a minimum, the risk of wildfires occurring when power lines touch vegetation is considerably reduced. This feature also enables continuous power supply during SLTE faults, increasing electricity system reliability. 

This thesis aimed to explore the potential use of VAG reactors as ASCs in medium-voltage distribution networks. To achieve this goal, a dynamic simulation model of VAG reactors was developed. In addition, two different controllers were created to optimize the behavior of the device during normal network operation and in the event of SLTE faults. Finally, the dynamic model of the VAG reactor was simulated using both control approaches in a realistic distribution network setting. The simulation results showed that the chosen approaches were effective in enhancing the reliability and safety of electricity distribution networks, thus demonstrating that VAG reactors could be a valuable tool in this regard.

Keywords: virtual air gap reactor, compensated networks, electric arcs, single-line-to-earth faults, earth-fault mitigation, electricity distribution systems, reliability

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53