The term 'Microshock' refers to a phenomenon in which transient electrical discharges occur through a small air gap between two electrodes at different potentials. Induced voltages on the human body can cause the discharges to people. It is the sensation caused by these discharges which is known as a 'microshock'. In a typical microshock, the current passing through the human body is tens of amps but its duration is few hundred nanoseconds. Microshocks are considered annoying and unpleasant even though their energy is well below the harmful threshold. Since information relating to microshock activity is limited, the main objective of this research is to better understand microshock activity and the perception of it by human beings. In particular it was intended to examine whether various physical scales of experimentation accurately represent the physical phenomena experienced by real people. The overall research consists of four parts: Firstly, an experimental setup was built in a small cage to investigate the characteristics of microshocks and to measure breakdown voltages with different electrode geometries, gap lengths, surface conditions and materials. Experimental outcomes show a 45% reduction of breakdown voltage with point-plane (r=0.20 mm) compared to sphere-plane (r=9.51 mm) electrodes. However this reduction is not proportional to the maximum electric field enhancement of 4.6 times the average. Significant reduction of breakdown voltage is seen when using meat electrodes. Moving electrodes show multiple discharges on closing and opening a gap, consistent with previous published work. The environmental conditions were also examined but showed no significant impact on breakdown voltage. Secondly, microshock discharge activities were examined in a controlled HV laboratory environment. Human perception to microshocks was investigated by carrying out a series of experiments first with a life-size model, and then with a real person. The relationships between the microshock voltage magnitude, the frequency of microshock occurrence, the conductor voltage, and the size of the air gap were analysed and suggest the importance of the number of half cycles of discharge on people's perception rather than the total number of discharges. Thirdly, experimental work was extended to an outdoor field environment, first with a model man and then with real people to understand the perception levels and microshock characteristics on people. Finally, a model was constructed using the PSCAD/EMTDC software package to study the characteristics of the microshock voltage waveforms and to model the experimental work with circuit theory. The four parts of the project are shown to give entirely consistent results. It is also shown that only when voltages above 1000 V are induced on people do they experience annoyance at microshocks. Above 2000 V microshocks become painful. Laboratory tests are shown to represent service conditions, and simple circuits may be used to model the discharge processes. Biological electrodes have been shown to create slightly different discharge characteristics which may account for variations in personal sensitivity to microshocks. This requires further investigation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:492234 |
| Date | January 2008 |
| Creators | Gunatilake, Aruna |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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