This thesis essentially presents the experimental investigation of the fundamental phenomena of electric fuse element disintegration and its causation and influence on the subsequent fragmentation of the fuse elements when subjected to excessive fault currents. The basis of the study involved experimental observation of disintegration of fuse elements and the analysis of the dynamic responses of current-carrying conductors, which precipitate disintegration. The experimental techniques employed utilised commercially available video cameras to capture images of element disruptions during disintegration of fuse elements subjected to low short-circuit and high overload currents. Specialist experimental image capturing techniques and hardware implementations were developed to enable investigation of element disintegration caused by high short-circuit fault currents. Disintegration phenomena of fuse elements for all fault cases were compared within different time domains, which included specialist techniques to investigate disintegration of elements in sand and against glass substrates. Disintegration phenomena of elements in unconfined media such as air and water also constituted the studies. The studies diverged, finally, into experimental observations of the temporal development of arc initiation and extinction phenomena of fault current limiting of HBC fuses using spectroscopic analysis of the arc light radiation. The range of studies covered have led to new understandings of fundamental current limiting behaviour of HBC and open type fuses which contribute, in a small way, to the knowledge base of the subject and hopefully will be an aid to improved designs and development of new types of electric fuse.

The objective of the proposed research is to quantify the limits of overstressed and aging circuit breakers in terms of probability of failure and to provide guidelines to determine network reconfigurations, generator commitment, and economic dispatch strategies that account for these limits. The proposed temporary power system operating strategies address circuit breaker adequacy issues and allow overstressed breakers to be operated longer and more reliably until they are replaced with adequate equipment. The expansion of electric networks with new power sources (nuclear plants, distributed generation) results in increased short-circuit or fault currents levels. As fault currents increase, they will eventually exceed circuit breaker ratings. Circuit breakers exposed to fault currents in excess of their ratings are said to be overstressed, underrated, or inadequate. Insufficient ratings expose overstressed breakers to increased failure probabilities. Extensive common-mode outages caused by circuit breaker failures reduce the reliability of power systems. To durably avoid outages and system unreliability, overstressed breakers must eventually be replaced. Large-scale replacements of overstressed breakers cannot be completed in a short time because of budgetary limits, capital improvement schedules, and manufacturer-imposed constraints. Meanwhile, to preserve the ability of old and overstressed breakers to safely interrupt faults, short-circuit currents must be kept within the limits imposed by the ratings and the age of these breakers by using the substation reconfiguration and generator commitment strategies described in this study. The immediate benefit of the above-mentioned operating strategies is a reduction of the failure probability of overstressed breakers obtained by avoiding the interruption of currents in excess of breaker ratings. Other benefits include (i) increased network reliability, (ii) restored operating margins with respect to existing equipment, and (iii) prioritized equipment upgrades that enhance the long-term planning of power systems.