A simple gas-blow switch, consisting of an axisymmetric tulip/pin contact and a cylindrical polytetrafluoroethylene (PTFE) nozzle, has been used for empirical studies of medium-voltage load current ...interruption in air. Only the thermal phase of the interruption is considered. Based on the results of more than 3000 interruption tests, a logistic regression model has been developed to describe the relationships between the switch design and test circuit parameters, and the current interruption capability. The most important design recommendation is that the inner diameter of the nozzle should be only slightly larger than the pin contact. The upstream overpressure needed for successful interruption increases as a polynomial function of degree 0.5-1 with the rate of rise of recovery voltage and of degree 2-3 with increasing current.
Levees are used in Australia and across the world as a structural means to reduce flood risks. However, people protected by levees can develop a false sense of security believing that the levee is ...fail-proof or might only fail in extreme flood events. This optimism can lower flood preparedness levels and lead to increased urban development in flood-prone areas. This can magnify flood risk behind the levee-a phenomenon known as the 'levee paradox' or 'levee effect'. This article analyses the results of a community survey conducted with residents and businesses located behind the levees in Launceston, Tasmania. The survey revealed a widespread low level of flood-risk awareness and elevated optimism about the protection afforded by the levee system. However, there were no significant and direct relationships between the possible levee paradox causal factors and the low levels of preparedness identified. This does not rule out the levee paradox, as more complex psychological interrelationships could be involved. Emergency management planning should consider the high proportion of people (over one-third) who stated they would require assistance during a flood in the Launceston leveeprotected areas.
As we observe in the moon-earth system, tidal interactions in binary systems can lead to angular momentum exchange. The presence of viscosity is generally regarded as the condition for such transfer ...to happen. In this paper, we show how the orbital evolution can cause a persistent torque between the binary components, even for inviscid bodies. This preferentially occurs at the final stage of coalescence of compact binaries, when the orbit shrinks successively by gravitational waves and plunging on a time-scale shorter than the viscous time-scale. The total orbital energy transferred to the secondary by this torque is ∼10−2 of its binding energy. We further show that this persistent torque induces a differentially rotating quadrupolar perturbation. Specializing to the case of a secondary neutron star, we find that this non-equilibrium state has an associated free energy of 1047-1048 erg, just prior to coalescence. This energy is likely stored in internal fluid motions, with a sizeable amount of differential rotation. By tapping this free energy reservoir, a pre-existing weak magnetic field could be amplified up to a strength of 1015 G. Such a dynamically driven tidal torque can thus recycle an old neutron star into a magnetar, with possible observational consequences at merger.
Air is an environmentally benign and attractive alternative to SF6 as arc quenching gas in switching devices for modest current and voltage ratings. Several interruption tests with a simple air ...medium-voltage load break test switch have been carried out to investigate the arc and the arcing voltage behavior for different circuit and switch design parameters. During the first half-cycle after contact separation, the arc voltage is typically 100 - 200 V. Approximately 50 μs before current zero the arc voltage increases in magnitude, before collapsing at current zero. The arc voltage increases with increasing contact gap, with decreasing current, and with increasing air flow. The arc voltage measurements from this work are believed to be suitable as experimental reference for verifying results from computational current interruption models.
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