Powerlines are important in the process of electricity transmission and distribution (T & D) and their essential role in transmitting electricity from the large generating stations to the final consumers cannot be over emphasized. Over the years, an increase in the demand for electrical energy (electricity) has led to the construction and inevitable use of high transmission voltage, sub-transmission voltage and distribution voltage power conducting lines, for the electricity T & D process. Along with this essential role, electricity conductors can also give rise to some electrically related effects such as interference with telecommunication circuits, electric shocks, electromagnetic fields, audible noise, corona ion discharges, etc.
The presence of powerline generated corona ions in any ambient air environment can be associated with the local modification of the earth’s natural dc electric field (e-field), while the interactions between these ions and other airborne aerosol particles can be associated with the presence of charged aerosol particles in the environment of the corona ion emitting lines. When considering all the studies conducted to date on the possible direct and indirect effects of high voltage powerlines (HVPLs), of significant interest are those suggesting links between powerlines and some adverse human health effects – with such health effects alleged to be strongest amongst populations directly exposed to HVPLs. However, despite the numerous studies conducted on HVPLs, to date a lack of proper scientific understanding still exist in terms of the physical characterization of the electrical environment surrounding real-world HVPLs - mostly in terms of the entire dynamics of ions and charged particles, as well as the possible links/associations between the different parameters that characterize these electrical environments. Yet, gaining a sound understanding about the electrical environment surrounding energized real-world HVPLs is imperative for the accurate assessment of any possible human exposure or health effects that may be associated with powerlines.
The research work presented in this thesis was motivated by the existing gaps in scientific understanding of the possible association between corona ions generated by real-world HVPLs and the production of ambient charged aerosol particles. The aim of this study was to supply some much needed scientific knowledge about the characteristics of the electrical environment surrounding real-world energized HVPLs. This was achieved by investigating the possible effects of corona ions generated by real-world overhead HVPLs on ambient aerosol particle number concentration level, ambient aerosol particle charge concentration level, ambient ion concentration level and the magnitude of the local vertical dc e-field; while also taking into consideration the possible effect of complex meteorological factors (such as temperature, pressure, wind speed wind direction, solar radiation and humidity) on the instantaneous value of these measured parameters, at different powerline sites. The existence of possible associations or links between these various parameters measured in the proximity of the powerlines was statistically investigated using simple linear regression, correlation and multivariate (principal component, factor, classification and regression tree-CART) analysis. The strength of the regression was tested with coefficient of determinations R2, while statistical significance was asserted at the 95 % confidence level.
For the powerline sites investigated in this study, both positive and negative polarities of ions were found to be present in the ambient air environment. The presence of these ions was associated with perturbations in the local vertical dc e-field, increased net ambient ion concentrations and net particle charge concentration levels. The mean net ion concentration levels (with a range of 4922 ions cm-3 to -300 ions cm-3) in the ambient environment of these powerlines, were in excess of what was measured in a typical outdoor air (i.e -400 ions cm-3). The mean net particle charge concentration levels (1469 ions cm-3 to -1100 ions cm-3) near the powerlines were also found to be statistically significantly higher than what was obtained for a mechanically ventilated indoor room (-84 ± 49 ions cm-3) and a typical urban outdoor air (-486 ± 34 ions cm-3). In spite of all these measured differences however, the study also indicated that ambient ion concentration as well as its associated effects on ambient particle charge concentration and e-field perturbations gradually decreased with increase in distance from the powerlines. This observed trend provided the physical evidence of the localized effect of real-world HVPL generated corona ions. Particle number concentration levels remained constant (in the order of 103 particles cm-3) irrespective of the powerline site or the sampling distance from the lines.
A close observation of the output signals of the sampling instruments used in this study consistently revealed large fluctuations in the instantaneous value of all the measured electrical parameters (i.e. non-periodic extremely high and low negative and positive polarities of ions/charged particles and e-field perturbations was recorded). Although the reason for these observed fluctuations is not particularly known at this stage, and hence in need of further investigations, it is however being hypothesized that, since these fluctuations appear to be characteristic of the highly charged environment surrounding corona ion emitting electrical infrastructures, they may be suggestive of the possibility that the release of corona ions by ac lines are not necessarily in the form of a continuous flow of ions.
The results also showed that statistically significant correlations (R2 = 74 %, P < 0.05) exists between the instantaneous values of the ground-level ambient ion and the ground-level ambient particle charge concentration. This correlation is an indication of the strong relationship/association that exists between these two parameters. Lower correlations (R2 = 3.4 % to 9 %, P < 0.05) were however found to exist between the instantaneous values of the vertical dc e-field and the ground-level ambient particle charge concentration. These suggest that e-field measurements alone may not necessarily be a true indication of the ground-level ambient ion and particle charge concentration levels. Similarly, low statistical correlations (R2 = 0.2 % to 1.0 %, P < 0.05) were also found to exist between the instantaneous values of ambient aerosol particle charge concentration and ambient ultrafine (0.02 to 1 μm sized) aerosol particle number concentration. This low level of correlations suggests that the source contribution of aerosol particle charge and aerosol particle number concentration into the ambient air environment of the HVPLs were different. In terms of the implication of human exposure to charged aerosol particles, the results obtained from this study suggests that amongst other factors, exposure to the dynamic mixture of ions and charged particles is a function of : (a) distance from the powerlines; (b) concentration of ions generated by the powerlines; and (c) meteorology - wind turbulence and dispersal rate.
In addition to all its significant findings, during this research, a novel measurement approach that can be used in future studies for the simultaneous monitoring of the various parameters characterizing the physical environment of different ion/charged particle emission sources (such as high voltage powerlines, electricity substations, industrial chimney stack, motor vehicle exhaust, etc.) was developed and validated.
However, in spite of these significant findings, there is still a need for other future and more comprehensive studies to be carried out on this topic in order to extend the scientific contributions of in this research work.
| Identifer | oai:union.ndltd.org:ADTP/265836 |
| Date | January 2008 |
| Creators | Fatokun, Folasade Okedoyin |
| Publisher | Queensland University of Technology |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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