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Title: Modelling of microshocks associated with high voltage overhead lines
Author: Ahmed, Yasir E.
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2009
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Microshocks can be described as the unpleasant discharges experienced by people capacitively coupled to high voltage equipment once a contact is established between their finger-tips and another object at different potential. The situations in which these discharges occur are complicated and very limited research has been conducted so far in this area. The work presented in this thesis aims to enhance the understanding of the microshocks phenomenon, and in particular, focuses on exposure to microshocks by overhead transmission line workers before developing mitigation techniques to prevent the linesman from receiving microshocks or at least minimising the sensation level associated with receiving the discharges. Results of a survey that included 102 linesmen and conducted to determine the implications of different factors on the frequency and intensity of microshocks are presented. Experimental setups and activities that took place inside and outside the High Voltage laboratory to simulate the environment at which linesmen became subjected to microshocks are discussed. Initially, a simplified 2-dimensional metallic test object "Stickman", which simulates a human body, was placed in various positions relative to a lattice tower structure inside the laboratory. Measurements of induced voltages and currents on the object as a result of capacitive coupling have been made. To accurately represent the structure and shape of the human body, a 3- dimensional test object "Cylinderman" has been designed and introduced to the experimental setup replacing Stickman. Experiments have been modelled successfully using the commercial software package CDEGS (Current Distribution and Electromagnetic Interference, Grounding and Soil Structure Analysis). The software package is shown to be capable of accurately modelling simple objects made of thin conductors as well as complicated structure such as the transmission tower. Furthermore, models of realistic and complicated scenarios under which linesmen experience Microshocks have been developed. Discharge voltage waveforms recorded of human subjects experiencing microshocks have been captured successfully. By examining these waveforms it was concluded that skin impedance dictates the level of voltage drop during discharge. In addition to investigating the effectiveness of earthing the body through the footwear to prevent microshocks from occurring, experiments that lead to the identification of a novel mitigation technique are detailed. The technique aims to increase the charging capacitance to ground -represented originally by the shoe capacitance- to reduce the induce voltage on the individual. Details of a filed patent are also included.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available