The suitability of N2 to replace SF6 in a triggered spark-gap switch for pulsed power applications

The high dielectric strength of sulphur hexafluoride (SF6) when compared with other gases, coupled with safety benefits such as non-flammability and non-toxicity, has seen the widespread use of SF6 for the insulation of switching components. However, SF6 is now widely recognised as a highly damaging greenhouse gas, and investigations of the switching properties of alternative gases to replace SF6 within the bounds of existing system topologies are required. In the present paper, a comparative study has been carried out on a triggered spark-gap of type presently deployed in industrial pulsed-power machines, to determine the suitability of nitrogen (N2) to replace SF6 as the switching medium, without compromising on functionality. Experiments were performed with fast-rising trigger pulses to minimise the delay time to breakdown and jitter, and three distinct operational regimes have been identified for both gases as the pressure inside the switch is increased. The static breakdown characteristics and upper pressure boundaries of operation have been determined for both gases at a range of dc charging voltages. Measurements of the time to breakdown have shown jitters as low as 1.3 ns when operating in N2, highlighting the potential of N2 to replace SF6 without the need for re-design or replacement of the presently used switch

Potential diversification benefits in the presence of unknown structural breaks: an Australian case study

The definitive version is available from http://www.blackwell-synergy.comIt is reasonable to suggest that a portfolio manager with direct property diversified by sector or region is more interested in strategic than in tactical asset allocation. However, even with strategic allocations of property the portfolio manager needs a regular monitoring of the inter-relationships amongst assets comprising the portfolio to ensure that unexpected events do not ‘permanently’ alter such relationships. One procedure for ascertaining whether assets are inter-related over the long run (and therefore offer few diversification benefits) is through cointegration analysis. A difficulty with conventional cointegration analysis, however, is that it is unable to accommodate changes in equilibrium relationships that might occur due to unexpected structural changes. In this paper we apply the Gregory and Hansen cointegration procedure to consider how unexpected structural changes might affect the potential long run diversification benefits of assets held in an Australian property portfolio