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The ageing of polymer insulation occurs under long-term exposure to high electric fields and has attracted research due its relevance to high voltage insulation. In this work, polymers that have been electrically aged via a number of methods have been investigated using X-ray photoelectron spectroscopy (XPS). Despite some use in the investigation of outdoor insulation surfaces, XPS has not been used for investigations of polymer bulk electrical ageing before now. The first XPS measurements, using both small spot analysis and XPS imaging, are presented from the exposed inner surfaces of electrically aged artificial voids and electrical breakdown channels, as well as corona discharge aged surfaces and spark discharge by-products. XPS is shown to be a valuable technique for the investigation of polymer electrical ageing. Investigations into breakdown channels are supported by data acquired using X-ray photoemission electron microscopy (XPEEM) and scanning electron microscopy (SEM).Results show that the chemistry present at these surfaces takes the form of significant oxidation over a wide area with localised production of graphitic carbon. C-O-, C=O, and O-C=O species are detected in all cases. It is found that similar ageing products are present regardless of the ageing process or material investigated. However, the level of oxidation and relative ratio of the species seen with XPS is shown to be highly dependant on oxygen availability. Greater intensity of carbon oxides, and a shift towards highly oxidised species, is observed when there is more oxygen in the system. XPS imaging of breakdown channels reveals that high concentrations of oxidised components form on the outer edges of the channel, with graphitic carbon forming in the central regions. In addition, evidence for degradation is seen to extend at least 300 μm from channels in XPS imaging and at least ~650 μm in XPS line scans. Variation with the applied discharge energy was investigated for breakdown channels and spark discharge ageing. Evidence is seen for an energy dependence on the breakdown products, with higher energies producing relatively higher graphitic carbon and reduced oxidation products. Further, the relationship between the applied voltage and graphitic carbon concentration suggests an activated process with an energy barrier before graphitic carbon formation starts. XPS observations are supported by confocal Raman microprobe spectroscopy (CRMS) results from artificial voids and electrical breakdown channels, which identify graphitic carbon on a fluorescent background as the main features. XPS data indicate oxidised species are the origin of the fluorescence seen and provides quantitative information on the levels, chemical states and spatial distribution of these species and of graphitic carbon.

The concept of More Electric Aircraft, where is to utilize the electrical power to drive more or all aircraft subsystem instead of conventional combination of pneumatic, hydraulic, mechanical and electrical power, can be recalled to World War II. It has been proven to have more advantages for decades in terms of energy efficiency, environmental issues, logistics and operational maintenance. It can also enhance aircraft weight, volume and battle damage reconfigurability.Thanks to the new electronics technologies and the emergence of new materials, It becomes feasible for high power density electrical power components to drive the majority of aircraft subsystem. However, sustaining the transmission of hundreds of kilowatts of electrical power at low voltages is not feasible owing to the penalties incurred due to high cable weights and voltage drop may become critical. It is very easy to come up with the solution of the increase of voltage. However, higher voltage will introduce other problems such as the reliability of insulation coordination on the aircraft due to the increased probability of electrical discharge. For aircraft designers, it is very important to understand the rules of insulation coordination on the aircraft including determining clearance and creepage distances, and also have a clear investigation of the phenomena and mechanism of electrical discharges. Past research has identified a number of the concerns of operating electrical systems at higher voltages in an aerospace environment, especially for dimensioning of clearances. However, there is little study on dimensioning of creepage distances and relevantly flashover and electrical tracking on solid insulating material surfaces. This thesis firstly discusses the rules for determining clearances and creepage distances. The experimental validation work was done for breakdown in air gap and on the solid insulating material surfaces under dry condition so that some standard recommended values can be evaluated not only with theoretical values such Paschen's law. Suggestions of application of those standards were provided. Secondly, the complex electrical discharge under wet condition on solid insulating material surfaces was discussed. A mathematical model to predict this type of electrical failure -electrical tracking (the electrical discharges on solid insulation materials which will lead to physical damage in the materials) with the consideration of different environmental conditions including air pressure, ambient temperature, and pollution degrees was developed. A series of electrical tracking tests were carried out on organic materials to find out the mechanism of electrical tracking and validate the finding by the mathematic model. Finite element analysis simulations were also conducted to find out the background thermal transfer mechanism to support our explanation of those phenomena of electrical tracking. Different test techniques have ben developed for specific impact factors. Finally, the suggestions for utilization of the standards and feasible test techniques for electrical tracking under wet conditions were provided.

A metamaterial (MTM) high power microwave (HPM) vacuum electron device (VED) was developed using 3D printing technology. The specific geometric pattern of the source can produce both negative permittivity and permeability to interact with a relativistic electron beam. The electron beam is generated using a pulsed electron accelerator with a maximum energy of 700 keV and lasting approximately 16 ns. The design of this novel VED consists of a circular waveguide loaded with complementary split-ring resonators in a linear periodic arrangement in which the relativistic beam travels guided by a magnetic field. The electrons interact with the MTM producing electromagnetic radiation, which is radiated to free space using a horn antenna. The HPM signal generated is characterized using a resistive sensor detector and a waveguide detector connected to a crystal diode. The radiation field distribution was measured using these detectors. Mode characterization is facilitated using an array of neon bulbs, which light up according to the intensity of the electric field. As a result, this excitation resembles the field pattern generated by the VED. The experimental results are compared with particle-in-cell (PIC) simulations and theoretical considerations.

At the interface of Power Electronics and High Voltage Engineering, this work combines theoretical considerations and experimental investigations to assess the endurance of polymeric insulation exposed to inverter-type medium-voltage stress, which is characterized by amplitudes in the kilovolt range, switching frequencies of several (tens of) kilohertz and slew rates of several kilovolts per microsecond.

Experimental Testing of a Metamaterial Slow Wave Structure for High-Power Microwave Generation by Kevin Aaron Shipman B.S., Exercise Science, University of New Mexico, 2008 A.S., Mathematics, San Juan College, 2014 M.S., Electrical Engineering, University of New Mexico, 2018 Abstract A high-power L-band microwave source has been developed using a metamaterial (MTM) to produce a biperiodic double negative slow wave structure (SWS) for interaction with an electron beam. The beam is generated by a ~700 kV, ~6 kA short pulse (~ 10 ns) electron beam accelerator. The design of the metamaterial SWS (MSWS) consists of a cylindrical waveguide, loaded with alternating split-rings that are linearly arrayed axially down the waveguide. The beam is guided down the center of the rings by a strong axial magnetic field. The electrons interact with the MSWS producing electromagnetic radiation in the form of high-power microwaves (HPM). The Power is extracted axially by a conical horn antenna. Microwave generation is characterized by an external cutoff waveguide detector, as well as the radiation pattern of the RF. Mode characterization is performed using a neon bulb array, where the bulbs are lit by the electric field in such a way that the pattern in which they are excited resembles the field pattern. A time integrated image is of this pattern is taken by an SLR camera. Since the MTM structure has electrically small features, breakdown within the device is a concern. Therefore, a fiber-optic-fed, sub-ns photomultiplier tube array diagnostic has been developed and used to characterize light emission from breakdown. A description of the diagnostic developed and experimental results will be presented.

We have developed a novel method of producing ultra-short channel graphene field effect devices on SiO2 substrates and have studied their electrical transport properties. A nonlinear current behavior is observed coupled with a quasi-saturation effect. An analytical model is developed to explain this behavior using ballistic transport, where the charge carriers experience minimal scattering. We also observe multilevel resistive switching after the device is electrically stressed. In addition, we have studied the evolution of the electrical transport properties of few-layer graphene during electrical breakdown. We are able to significantly increase the time scale of break junction formation, and we are able to observe changes occurring close to breakdown regime. A decrease in conductivity along with p−type doping of the graphene channel is observed as the device is broken. The addition of structural defects generated by thermal stress caused by high current densities is attributed to the observed evolution of electrical properties during the process of breakdown. We have also studied the effects of the local environment on graphene devices. We encapsulate graphene with poly(methyl methacrylate) (PMMA) polymer and study the electrical transport through in situ measurements. We have observed an overall decrease in doping level after low-temperature annealing in dry-nitrogen, indicating that the solvent in the polymer plays an important role in doping. For few-layer encapsulated graphene devices, we observe stable n−doping. Applying the solvent onto encapsulated devices demonstrates enhanced hysteretic switching between p and n−doped states.

Massively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore, it is essential to selectively remove metallic nanotubes to obtain better transistor properties. It was recently found that although such a selective removal can be effective for a low density array, it does not work in a high density array and lead to a correlated breakdown of the entire array giving rise to a nanofissure pattern. In order to obtain a deeper understanding of such a correlated SWNT breakdown, we studied the breakdown power in the successive electrical breakdown of both low ( < 2 /um) and high density ( > 10 /um) SWNT arrays. We show that the breakdown voltage in successive electrical breakdown increases for low density array while it decreases for high density arrays. The estimated power required for the breakdown remains constant for low density arrays while it decreases for high density arrays in successive electrical breakdowns. We also show that, while a simple model of parallel resistor network can explain the breakdown of low density array, it cannot explain the behavior for the high density array implying that the correlation between the closely spaced parallel nanotubes plays a big role in the successive breakdowns of the high density SWNTs.