The transition away from SF6-based insulation in high-voltage equipment has accelerated interest in alternative gas mixtures with lower environmental impact. One such mixture is CO2/O2 (70%/30%), which is used as a carrier gas in C4-FN based mixtures but is also being explored for stand-alone insulation applications. To enable detailed characterisation of partial discharges (PDs) in such alternative gases, a high-bandwidth measurement setup was developed. The setup is based on a custom designed test compartment that uses a needle-to-plane electrode configuration to generate corona discharges and applies a high-frequency current transformer (HFCT) as a measurement impedance.
Initial measurements using a conventional IEC 60270 configuration revealed a resonance frequency of 3.5 MHz, which limited the effective bandwidth of the system. By eliminating the traditional coupling capacitor and instead using the inherent capacitance between the conductor in the bushing and the grounded enclosure as a coupling path, the resonance frequency was shifted to 144 MHz. Aside from the significant increase in bandwidth, this also improved sensitivity. The frequency response of each segment of the measurement circuit was characterised, allowing the derivation of the PD current from the measured voltage and enabling calibration-free charge estimation. The setup was used to study the PD behaviour in a CO2/O2 (70%/30%) mixture at pressures ranging from 0.2 to 0.4 MPa and voltages up to 1.5 times the PD inception voltage. A novel phenomenon was observed: certain PDs were rapidly followed by another discharge, after which a longer interval was required for the next event.
Multiple charge estimation methods were adapted to suit the measurement circuit. After evaluation, the modified frequency domain method demonstrated the strongest correlation with peak current, especially at low discharge magnitudes. These results demonstrate that the developed measurement setup is suitable for detailed PD analysis in alternative gases and that it is able to offer new insight into the behaviour of alternative gases.

Many overhead transmission lines in the Netherlands are multi-circuited; when one circuit is de-energized for maintenance, the other remains energized. The energy transition necessitates more transmission line reinforcements and heavier loading of existing lines to meet the increasing power demand, consequently increasing the need for additional linework. The energized circuit induces a voltage (EMF) and current in the circuit being worked on. As a further safety measure, line workers utilize a portable earthing device (PED) that is attached to the de-energized circuit’s conductors. The induced voltage and current in the circuit can cause arcs up to half a meter long when attaching or detaching the PED, posing a serious threat to workers’ safety. There are no active mechanisms in place to stop the arc, so it must naturally extinguish in air.

This thesis aims to model and characterize naturally extinguishing arcs in air. There is little available literature on this topic, which primarily consists of models for static free-burning arcs in air. There are two key objectives in this research: (1) develop a mathematical expression describing the behaviors of naturally extinguishing arcs in air and (2) use the derived expression to produce an arc model simulation verifying the expression’s validity and accuracy. The provided test data, including arc videos and oscilloscope data, encompassed arcs under various testing conditions and utilized a test setup that mimicked the arcing environment of a PED being detached from a conductor. The arc distances were approximated using MATLAB image processing techniques due to the videos’ poor quality in showcasing the arc distances. These approximated arc distances and oscilloscope data were examined and manipulated to develop an overarching arc expression that represents the resistance-current relationship evident in free-burning arcs in air. Two expressions were derived for comparison: a logarithmic expression and a power law expression. These expressions were implemented in two separate ATP-EMTP software models that each utilized a MODELS-language module to represent the arc for simulation.

The resulting resistance and voltage-current characteristics of the two models were compared against the original test data. The power law expression was found to be the more accurate of the two models. Different testing conditions were then applied to the arc model to identify their natural arc extinction distances, which were also compared against the original test data. The results establish that the power law expression arc model sufficiently predicts the natural arc extinction distance. These predictions can be improved in the future with more precise test data. This thesis’s research fills a gap in the existing literature on modeling natural arc extinction in air. The findings of this research can influence future safety procedures for the line workers who experience these arcs. Furthermore, the results of the arc model for PED removal can potentially be expanded to describe the arcing behavior of disconnectors during bus transfer assessment, leading to a greater understanding of disconnectors and providing a deeper insight into their application and test result interpretations.

The emergence of electric mobility in urban public transportation, with a particular focus on electric buses, presents a promising solution to address emissions and environmental concerns. However, a significant challenge lies in ensuring continuous bus operation without the need for frequent charging. In-motion charging (IMC), often referred to as dynamic charging, is a concept engineered to overcome this challenge.

A comprehensive study was undertaken to know the potential and practicality of intercity IMC buses. A bus model was developed to assess the power traction capabilities of these vehicles. This model served as the foundation for exploring four distinct charging scenarios, each characterized by varying charging powers and strategies. An investigation into the battery load profiles observed in intercity IMC buses across the different charging scenarios was done. This was essential for understanding the intricacies of power demand, especially in scenarios where the bus relies heavily on catenary charging. Notably, the introduction of in-motion charging in the first scenario (IMC only) underscored the critical role of catenary charging power in meeting operational demands. Subsequent integration of a stationary charging system at Arnhem Central showcased the potential to reduce catenary charging power, offering prospects for enhancing battery health. IMC with opportunity charging and overnight charging were also explored.

The second part of the thesis delved into the comparative effect of various charging scenarios on the aging of commonly employed battery chemistries in IMC vehicles. Using comprehensive battery models, the aging dynamics under diverse conditions were studied. It became evident that each scenario held distinct implications for battery aging.

Lastly, the study addressed the pivotal question of cost-effective battery selection for intercity IMC buses. An exploration of four distinct scenarios, in conjunction with different battery chemistries, yielded valuable insights into their respective performances. Lithium-titanate (LTO) batteries consistently emerged as the preferred choice. Their extended lifespan, reduced replacement frequency, and overall cost-effectiveness positioned them as the frontrunners in the context of intercity IMC bus systems. This consensus held across most scenarios, underscoring the practicality of LTO batteries.

In conclusion, the transportation sector's substantial impact on greenhouse gas emissions and urban air quality necessitates innovative and sustainable solutions. Intercity IMC buses, along with optimal battery selection and charging strategies, represent a promising avenue for sustainable urban transportation. Among battery chemistries, LTO batteries was proven to be the most cost-effective choice for powering intercity IMC bus operations.