Performance of uprated substations in contaminated environments

Uprated substations have proven to be a viable economic alternative to rebuilding in order to increase power system capacity. The key economic factor in uprated designs is the use of lower than traditional insulation margins in high voltage substations. The experience of these uprated substations has been good and insulation design procedures for uprated substations have been developed to show other engineers how to take advantage of this design alternative. While these design procedures and other publications including the results of actual tests have given ample evidence of the success of the uprated designs, it has been noted that several areas need more study and testing. Among those areas which need further study are the effects of the dynamic forces caused by higher fault currents in the uprated substations and the ability of the reduced creepage distances of the uprated design to withstand pollution severity. This study covers the pollution severity issue by examining the results of flashover tests on the uprated substation insulators under various contamination conditions. The tests, which were done at the EPRI Power Deliver Center at Lenox, USA, are believed to be the only flashover tests ever conducted with uprated insulators. As might be expected, the uprated design is shown to be very sensitive to pollution severity. Sites chosen for uprating should include a pollution severity assessment as part of the design review     

Pollution severity performance chart; key to just-in-time insulatormaintenance

Determining when to take corrective action on contaminated high voltage insulators has been a problem for electric utilities for many years. In particular, the setting of realistic threshold levels to trigger corrective action has been very difficult. This problem has become even more important because of the need for better utilization of field personnel as a result of the continuing downsizing and re-engineering of electric operating companies. There has been a renewed interest in predictive monitoring devices that can initiate just in time maintenance. This interest includes pollution monitoring devices. This paper is based on a study of both the evaluation of pollution monitors as well as actual flashover tests. Because of the statistical nature of insulator flashovers and the relative few that occur in operating companies it is necessary to conduct laboratory flashover tests to determine threshold levels. This study was done for a specific electric utility but does indicate a process for establishing procedures for other utilities to develop programs for determining when they should take corrective action on contaminated insulators     

Transient process in ice creams evaluated by laser speckles

When a coherent light beam is scattered from a colloidal medium, in the observation plane, appears a random grainy image known as speckle pattern. The time evolution of this interference image carries information about the ensemble-averaged dynamics of the scatterer particles. The aim of this work was to evaluate the use of dynamic speckles as an alternative tool to monitoring frozen foams formulated with glucose and fructose syrups. Ice creams, after preparation and packing, were stored at ?18 °C. Changes in properties of products were analyzed by speckle phenomena at three room temperatures (20 °C, 25 °C and 30 °C), minute by minute, during 50 min. Two moments were identified in which samples activity achieved significant levels. These instants were associated, respectively, to ice crystals melting and to air bubbles dissipation into the food matrix causing motion of diverse structures. As expected, ice crystals melting was first in formulations containing fructose syrup, but for same samples, air losses were delayed. Speckle methodology was satisfactory to observe temporal evolution of transient process, opening goods prospects to application, still incoming, in foodstuffs researches.     

Tuning the pH Response of i‐Motif DNA Oligonucleotides

Cytosine‐rich single‐stranded DNA oligonucleotides are able to adopt an i‐motif conformation, a four‐stranded structure, near a pH of 6. This unique pH‐dependent conformational switch is reversible and hence can be controlled by changing the pH. Here, we show that the pH response range of the human telomeric i‐motif can be shifted towards more basic pH values by introducing 5‐methylcytidines (5‐MeC) and towards more acidic pH values by introducing 5‐bromocytidines (5‐BrC). No thermal destabilisation was observed in these chemically modified i‐motif sequences. The time required to attain the new conformation in response to sudden pH changes was slow for all investigated sequences but was found to be ten times faster in the 5‐BrC derivative of the i‐motif.     

Human resources and scientific productivity in Brazil

The number of Brazilian scientific publications increased from 0.29% to 0.56% of the worldwide total during the 1981–1993 period. There was a decrease of the funds allocated to most scientific activities, except for that allocated for training of new scientists. The numbers of research fellowships and scientific publications increased at the same ratio during the period. The pattern of scientific publications and the number of fellowship granted along the years in the different fields of research were analyzed. The data presented indicate that even in a period of economic crisis, a selective investment of funds in human resources may lead to an increase of the scientific productivity of a country in all science fields.     

Global analysis of the phase calibration operation

A global approach to phase calibration is presented. The corresponding theoretical framework calls on elementary concepts of algebraic graph theory (spanning tree of maximal weight, cycles) and algebraic number theory (lattice, nearest lattice point). The traditional approach can thereby be better understood. In radio imaging and in optical interferometry, the self-calibration procedures must often be conducted with much care. The analysis presented should then help in finding a better compromise between the coverage of the calibration graph (which must be as complete as possible) and the quality of the solution (which must of course be reliable).