Contamination, electrical breakdown

Moisture. The effects of moisture degradation are more pronounced with resistance, dissipation factor, and capacitance than with breakdown. Functionally, the effect of moisture on the electric breakdown may be disastrous. High relative rather than absolute humidity is the causative factor. At higher temperatures the rate of moisture permeation increases. Moisture condensation on plastic surfaces, especially in the presence of ionizable or carbonizing contaminants, may be an important source of degradation. Surface flashover may occur almost instantaneously with moisture condensation, whereas volume breakdown develops after weeks or months. 

Lubricating oil analysis, as the name implies, is an analysis technique that determines the condition of lubricating oils used in mechanical and electrical equipment. It is not a tool for determining the operating condition of machinery. Some forms of lubricating oil analysis will provide an accurate quantitative breakdown of individual chemical elements, both oil additive and contaminates, contained in the oil. A comparison of the amount of trace metals in successive oil samples can indicate wear patterns of oil wetted parts in plant equipment and will provide an indication of impending machine failure. 

Not all of the evidence was sound because the early analytical methods for DDT using gas chromatography could confuse PCBs (polychlorinated biphenols) and DDT breakdown products, ffowever, these analyses alerted scientist and the public to the widespread contamination of the environment with PCBs (widely used in electrical transformers and other industrial equipments at that time but subsequently banned), which became a new concern. 

The electric strength or dielectric breakdown test method (ASTM D-877) indicates the absence, or presence, of free or suspended water and other contaminant matter that will conduct electricity. A high electric strength gives no indication of the purity of an oil in the sense of degree of refinement or the absence of most types of oil-soluble contaminants. This test method is of some assistance, when applied to an otherwise satisfactory oil, to indicate that the oil is free of contaminants of the type indicated above in practice, this ensures that the oil is dry. 

Test (he electrical properties (resistivity and or permittivity) of the immersion liquid to be used. Contamination of the liquid can often lead to erroneously high breakdown voltage values. 

Another important advantage of MR fluids is their relative insensitivity to temperature changes and contamination. This arises from the fact that the magnetic polarization of the particles is not influenced by the presence or movement of ions or electric charges near or on the surface of the particles. Surfactants and additives that affect the electrochemistry of the fluid do not play a role in the magnetic polarizability of the particles. Further, bubbles or voids in the fluid can never cause a catastrophic dielectric breakdown in an MR fluid. 

If an ionic path is present between two oppositely biased metal lines that are otherwise isolated and the path resistance is adequately low, then sufficient voltage will exist to enable an electrical current to flow between the lines (Fig. 4a). A portion of the applied voltage difference will exist at each metal-electrolyte interface, permitting electrochemical oxidation/reduction reactions to occur. The extent of the resulting corrosion depends on many factors, but the resistance of the ionic pathway is the most important. The influence of increasing moisture and contamination on decreasing the ohmic resistance of the ionic path is further explained by Osenbach [17] and has been phenomenologically modeled by Comizzoli [46], Contamination has a further role because of its effect on the breakdown of the passive oxide on many metals. 

Metallic contamination can alter the electrical properties of the semiconductor devices. These ions can diffuse into the substrate (such as silicone oxide) during subsequent heat treatment, causing drifts in surface potential, current leakage, structural defects in vapor-grown epitaxial layers, and reduced breakdown voltage of gate oxides. 

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