Abstract: This paper investigates the effects of breaks in bonds,
breaks in the earthing system and breaks in earth wire on the rise of
the earth potential (EPR) in a substation and at the transmission tower
bases using various models of an L6 tower. Different approaches
were adopted to examine the integrity of the earthing system and the
terminal towers. These effects were investigated to see the associated
difference in the EPR magnitudes with respect to a healthy system at
various locations. Comparisons of the computed EPR magnitudes
were then made between the healthy and unhealthy system to detect
any difference. The studies were conducted at power frequency for a
uniform soil with different soil resistivities. It was found that full
breaks in the double bond of the terminal towers increase the EPR
significantly at the fault location, while they reduce EPR at the
terminal tower bases. A fault on the isolated section of the grid can
result in EPR values up to 8 times of those on a healthy system at
higher soil resistivities, provided that the extended earthing system
stays connected to the grid.
Abstract: A supersonic expansion cannot be achieved within a convergent-divergent nozzle if the flow velocity does not reach that of the sound at the throat. The computation of the flow field characteristics at the throat is thus essential to the nozzle developed thrust value and therefore to the aircraft or rocket it propels. Several approaches were developed in order to describe the transonic expansion, which takes place through the throat of a De-Laval convergent-divergent nozzle. They all allow reaching good results but showing a major shortcoming represented by their inability to describe the transonic flow field for nozzles having a small throat radius. The approach initially developed by Kliegel & Levine uses the velocity series development in terms of the normalized throat radius added to unity instead of solely the normalized throat radius or the traditional small disturbances theory approach. The present investigation carries out the application of these three approaches for different throat radiuses of curvature. The method using the normalized throat radius added to unity shows better results when applied to geometries integrating small throat radiuses.