Browsing by Author "Jojozi, Mbulelo"

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    Investigation of the stability of short arcs
    (2002) Jojozi, Mbulelo; Gaunt, C Trevor
    The research described in this thesis is an investigation of stability of short arcs. It is on fault tolerant medium voltage distribution networks. It serves to describe experimental findings of the investigation of stability of short (1000mm) arcs. The instability of short arcs with high source impedance may be exploited to improve the lightning performance of medium voltage distribution lines. Lightning initiated flashovers on distribution networks do not necessary lead to power follow current. This subject has been the cause for concern to various authors as far back as the 1930 and 1940. But from the literature search that has been done in this thesis there is not enough information about the effect of high source impedance on arc quenching. A thorough literature search has been done to establish work that has been done by these authors. Some work was reported by Darveniza [1], but without details of the dynamic response. Most of the work on arc quenching and electric properties of wood was done by Darveniza [1]. Various developed arc-quenching techniques are highlighted in this document. The arc behaviour is then discussed without going into the details of plasma physics. The general characteristics and dynamics of AC arcs that are discussed include inter alia the voltage versus current (V-I) characteristic, extinction methods under different circuit parameters and re-ignition of arcs as discussed by Cobine [33]. A range of tests were performed in the newly built medium voltage laboratory at the University of Cape Town. Preliminary tests at low voltage (230V) were performed to establish the possible trends of the arc behaviour and from which the measurement and control circuits were established. This involved initiating an arc channel at different voltages up to 40kV in air and along wood surface path.