A technique was developed for the comparison of observed emission spectra from lightning current arcs generated through self-breakdown in air and the use of two types of initiation wire, aluminum bronze and nichrome, against previously published spectra of natural lightning events. A spectrograph system was used in which the wavelength of light emitted by the lightning arc was analyzed to derive elemental interactions. A lightning impulse of up to 100 kA was applied to a two hemispherical tungsten electrode configuration which allowed the effect of the lightning current and lightning arc length to be investigated. A natural lightning reference spectrum was reconstructed from literature, and generated lightning spectra were obtained from self-breakdown across a 14.0 mm air gap and triggered along initiation wires of length up to 72.4 mm. A comparison of the spectra showed that the generated lightning arc induced via self-breakdown produced a very similar spectrum to that of natural lightning, with the addition of only a few lines from the tungsten electrodes. A comparison of the results from the aluminum bronze initiation wire showed several more lines, whereas results from the nichrome initiation wire differed greatly across large parts of the spectrum. This work highlights the potential use for spectrographic techniques in the study of lightning interactions with surrounding media and materials, and in natural phenomena such as recently observed ball lightning.

A recently developed spectrographic technique was used for the comparison of observed optical emission spectra from self-breakdown in air of high current and high voltage impulse arcs which are often used to represent the respective components of a natural lightning strike for a variety of lightning studies. These components are separated as it is practically impossible to simultaneously generate both in a single arc within the laboratory. The high current aspect is typically related to the amount of damage a lightning arc does to an impacted object and can be used to characterize conductivity properties, whereas the high voltage aspect is typically related to the attachment mechanism of lightning to an object when creating a path to ground and can be used to characterize insulation properties. The spectra of a range of high current arcs up to 100 kA and high voltage arcs up to 120 kV across a 14 mm air-gap between a pair of hemispherical tungsten electrodes were investigated and compared with the natural lightning reference spectrum reconstructed from the literature. All three spectra were found to present similar trends, but the high voltage arc had notably lower blackbody radiation, indicating a less energetic and cooler arc. Further, whereas atomic lines from oxygen and nitrogen were clearly present, an atomic line from argon was not prominent, indicating that the bulk energy delivered into the air was in the range of 1400–1520 kJ/mol. The high current arc, much like natural lightning, delivered a bulk energy greater than 1520 kJ/mol.

The research in this paper consists of practical experimentation on a gas insulated section of high voltage equipment filled with carbon dioxide and technical air as a direct replacement to sulphur hexafluoride (SF₆) and analyses the results of PD measurement by way of internal UHF sensors and external HFCTs. The results contribute to ongoing efforts to replace the global warming gas SF₆ with an alternative such as pure carbon dioxide or technical air and are applicable to mixtures of electronegative gases that have a high content of buffer gas including carbon dioxide. The experiments undertaken involved filling a full-scale gas insulated line demonstrator with different pressures of CO₂ or technical air and applying voltages up to 242 kV in both clean conditions and particle contaminated conditions. The results show that carbon dioxide and technical air can insulate a gas section normally insulated with SF₆ at phase-to-earth voltage of 242 kV and that both HFCT and UHF sensors can be used to detect partial discharge with natural gases. The internal UHF sensors show the most accurate PD location results but external HFCTs offer a good compromise and very similar location accuracy.

This paper uses practical experimentation to analyse the effect of replacing SF₆ with pure CO₂ in conventional gas insulated transmission line sections by studying partial discharge measurements taken with applied voltages up to 242 kV (rms). The results can also help in understanding the properties of new alternative gas mixtures which can be utilised with a ratio of up to and over 95% CO₂. The experiments undertaken involved filling a gas insulated line demonstrator with 3 bars of CO₂ and applying voltages up to 242 kV in both clean conditions and particle-contaminated enclosure conditions. The results demonstrate that CO₂ can be used to insulate gas equipment without breakdown at high voltage, however, a higher gas-filling pressure may be needed to reduce the partial discharge found in the tests presented in this paper. Another aspect of the work showed that partial discharge (PD) measurements from internal ultra-high frequency (UHF) sensors compared with a direct measurement from a capacitive divider both clearly showed the effect of contaminating particles in CO₂. However, the PD divider measurements also showed considerable external PD on the outside of the gas compartment, leading to the conclusion that UHF sensors are still regarded as having the highest sensitivity and noise immunity for gas insulated switchgear (GIS) or gas insulated transmission line (GIL) systems including when the equipment is insulated with CO₂.

Predictors of people's responses to noise inside cars are used by car companies to identify and address potential noise problems from tests. Because significant improvements have been made in engine, powertrain, and tire/road noise, it is now important to pursue improvements in wind or aerodynamic noise. While models of loudness are commonly used to predict people's responses to stationary wind noise, some wind noises are less acceptable than is predicted by loudness metrics. Additional sound characteristics may account for this. Three listening studies were designed to examine the usefulness of including additional sound quality metrics with loudness in models used to predict acceptability for stationary wind-noise sounds. Test sounds were based on recordings made in cars in a wind tunnel. Signal modification techniques were developed to decorrelate metrics across a set of sounds and to examine how acceptability changes with strengths of particular sound characteristics. Models of acceptability for stationary wind noise are significantly improved when a metric that predicts the sharpness of a sound is included in the model with the loudness metric.

Automobile manufacturers are trying to improve the interior noise environment in their cars. A more thorough understanding of how people perceive the noise is an important step towards this goal. The focus of the current research is on modeling the acceptability of time-varying wind noises containing gusts. A listening test was designed containing sounds that were simulated on the computer, based on pre-defined airflow profiles. The time-varying noises in the test follow one of two simple gusting scenarios. The primary scenario contained two segments of steady wind flanking a series of consecutive equal-strength gusts. The number, duration, and strength of the gusts were varied between sounds. This was done to examine general trends of acceptability with modulation rate, modulation depth, and duration. The second scenario contained two gusts of equal or unequal strength, occurring either without a break or separated by a time gap. This was done to examine the relationship between people's reactions to the individual gusts in a pattern and their reactions to the whole pattern. A small number of steady-wind noises were included for reference. Terms in an acceptability model containing a previously proposed gusting metric were estimated. Possible refinements to the metric and model are discussed.