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Long-term degradation and dielectric breakdown of large bandgap insulators is caused by a complex set of mutually influenced microscopic physical and chemical mechanisms. Electronic, thermal, chemical, mechanical and other effects cannot be separated a priori and the lifetime-limiting processes have to be established in each case under specified conditions, for a given material system. In this short...
It is generally accepted that dielectric ageing, prebreakdown and breakdown in solid dielectrics are initiated at points of high local field (1). The damage process depends very much on the way the system reacts to the local field enhancement. To make this point clear we discuss a simple example. We consider a simple needle-plate geometry. We furthermore assume that the current density versus local...
The build up of space charge above a critical field strength, Fc, can be regarded as an important mechanism for electrical tree nucleation and ageing [1]. For voltage ramps of msec, a homogeneous space charge cloud grows instantaneously if Vc, the voltage at which F = Fc, is surpassed. As a consequence, F will never be exceeded: we deal with field limiting space charge (FLSC model of ref. 1+2). Within...
EPA has developed guidance for a tiered approach to ocean disposal monitoring that includes the following major elements: [1] A heirarchy of monitoring tiers including compliance, nearfield, farfield, marine resources, and ocean processes, [2] Regulatory and environmental endpoints and related null hypotheses for each tier, [3] An iterative process of predicting and field testing disposed waste transport,...
For a long time treeing has been known as a major mechanism responsible for ageing of technical insulations, which can subsequently lead to their catastrophic breakdown. According to its importance, treeing is the subject of a vast number of publications /1/. Tree initiation and the conditions for tree growth, however, have been studied to a much lesser extent. In a recent paper /2/ this problem is...
Space charges are known to play a very important role in dielectric ageing. The difference between impulse and dc electric strength, the influence of prestressing and impulse rise time on breakdown voltages and the polarity dependence of the breakdown voltage in the needle plate geometry all have been explained by space charge build up (1). In addition, the action of highly energetic charge carriers...
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