Insulators, degradation

By comparison with I C equipment, cable aging is dependent upon the type of cable (e.g., whether or not it is armored), the type of insulation (e.g., some types of insulation degrade more rapidly when exposed to sunlight), the potential for mechanical or thermal damage, and humidity. It is also a function of cable loading, and environment. Cable joints can be a weakness. However, 60-year-old operational cables are not unknown. 

Insulation characteristics Inspections of the failed power transformers revealed heat failure, mostly because of paper insulation degradation. GIC can cause immediate or delayed power transformer outage. In the second case, power transformer outage is the result of several solar storms impacts. The diagnostics mechanism with the means of Duval triangle is described in (Gaunt, Charles Trevor 2014). 

A mechanical failure, for example, could occur as the result of an impact between a ship and another moving vessel or a stationery object. An electrical failure could occur as the result of internal partial discharges that degraded the insulation of a ship s propulsion motor. A chemical failure could occur as the result of corrosion of poorly protected parts/components on an offshore wind turbine. Finally, a thermal failure could be the result of heat generated by current flowing in an electrical conductor, causing insulation degradation. 

G. Mascolo, O. Marina, and V. SabatelU, Refractory and insulation degradation in an oil-fired power plant, Sci. Ceram, 12 411,1984. 

Protective Coatings. Some flame retardants function by forming a protective Hquid or char barrier. These minimize transpiration of polymer degradation products to the flame front and/or act as an insulating layer to reduce the heat transfer from the flame to the polymer. Phosphoms compounds that decompose to give phosphoric acid and intumescent systems are examples of this category (see Flame retardants, phosphorus flame retardants). 

Storage tanks, lines, and pumps should be heat traced and insulated to enable product handling. Temperature control is required to prevent product degradation because of color alkan olamines have poor heat transfer properties. Exposure to air will also cause product discoloration. Storage tanks should be nitrogen-padded if low color product is required. 

The most important properties of refractory fibers are thermal conductivity, resistance to thermal and physical degradation at high temperatures, tensile strength, and elastic modulus. Thermal conductivity is affected by the material s bulk density, its fiber diameter, the amount of unfiberized material in the product, and the mean temperature of the insulation. Products fabricated from fine fibers with few unfiberized additions have the lowest thermal conductivities at high temperatures. A plot of thermal conductivity versus mean temperature for three oxide fibers having equal bulk densities is shown in Figure 2. 

Finishes Thermal insulations require an external covering (finish) to provide protection against entry of water or process fluids, mechanical damage, and ultraviolet degradation of foamed materials. In some cases the finish can reduce the flame-spread rating and/or provide fire protection. 

The effective therm conductivity values generally obtained in practice are at least a factor of two greater than the one-dimensional thermal conductivity values measured in the laboratoiy with carefully controlled techniques. This degradation in insulation thermal performance is caused by the combined presence of edge exposure to isothermal boundaries, gaps, joints, or penetrations in the insulation blanket required for structure supports, fill and vent hnes, and high lateral thermal conductivity of these insulation systems. 

Homma, H., Kuroyagi, T., Izumi, K., Mirley, C.L., Ronzello, J. and Boggs, S.A., Evaluation of surface degradation of silicone rubber using thermogravimetric analysis, Proc. Int. Symp. Electr. Insul. Mater., 2nd. 1998, 1, pp. 631-634. 

The source of ignition of the polyethylene glycol was probably autoignition of the degraded material. The report recommends the use of nonabsorbent insulation for equipment containing heat-sensitive materials such as EO [19, 20]. 

Ensure that the insulation selected can operate effectively and without degradation at temperatures beyond the design temperature called for. Temperature control of the process system can fail and systems can overheat. Hot surfaces exposed to ambient air will become hotter when insulated if there is no control of the process temperature. As with multi-layer systems, the addition of an extra layer... 

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