The most common fault type in electric power systems is the line to groundfault. In this type of faults, an electrical arc is usually developed. The thesispresents a mathematical model that describes the behavior of the arc during afault. The arc model has been verified based on real and simulated tests thatwere conducted on a system that has resonant earthing coil.In addition, two studies have been conducted on the same verified system.The first studied was implemented to see the effect of detuning the resonantearthing coil at different levels. It was noted that detuning the coil affected ACand the DC components in the arc faults. Also, the detuning affected the arcextinction.The second study has been looking at the effects of implementing a parallelresistor to the resonant earthing coil. The tests have been conducted usingdifferent set values of the resistor. In some of the studied cases and during thetesting period, the resistor has affected the self-extinguish behavior of the arc. / Den vanligaste feltypen i elektriska kraftsystem är fas till jord. I denna typ avfel utvecklas vanligtvis en elektrisk ljusbåge. Examensarbetet presenterar enmatematisk modell som beskriver ljusbågens beteende under ett fel. Bågmodellenhar verifierats baserat på verkliga tester och simuleringar som utfördespå ett system som har resonansjordningsspole.Dessutom har två studier genomförts på samma verifierade system. Denförsta studien genomfördes för att se effekten av avstämning av den resonantajordningspolen på olika nivåer. Det noterades att avstämning av spolen påverkadeACoch DC-komponenterna i ljusbågsfel.Avstämningen påverkade ocksåljusbågens släckning.Den andra studien har tittat på effekterna av att implementera ett parallelltmotstånd till den resonanta jordningsspolen. Testen har utförts med olikainställda värden på motståndet. I några av de studerade fallen och under testperiodenhar motståndet påverkat ljusbågens självsläckande beteende.

Current practice in U.S. underground coal mine high-voltage distribution systems is to attempt to limit ground fault current to 25 Amperes and de-energize the circuit at 10 Amperes. However, the significant amount of system capacitance due to the use of shielded cables can cause ground fault current to be two or three times the intended ground fault limit. Consequently, this practice can cause several issues such as ground fault currents significantly exceeding the neutral grounding resistor current limit, loss of relay selectivity in the distribution system, and transient overvoltages in certain ground fault situations. These issues are solved to some extent by using a resonance grounded system, currently used in some other countries. However, a shortcoming of traditional resonance grounded systems is the inability to deal with the harmonic components existing in ground fault current. With the increasing use of nonlinear sources such as variable frequency drives, the proportion of harmonic components in ground fault current can be significant. Consequently, although the fundamental component can be almost fully compensated in a traditional resonance grounded system, the harmonic components can still be large enough to maintain arcing and cause personal injury and equipment damage. In this dissertation, a novel method is developed to perform real-time prediction of the harmonics in ground fault currents. Methods for neutralizing the ground fault current harmonics and identifying ground fault location are also developed. Results indicate that the combination of traditional high-resistance grounding and active current injection to neutralize harmonics in the ground fault has the potential to significantly reduce the total ground fault current and reduce arc and flash hazards during ground faults in high voltage distribution systems.