Insulation system selection

Air-Atmosphere Furnaces. These furnaces are appHed to processes where the workload can tolerate the oxidation that occurs at elevated temperatures in air. In some special appHcations, the oxidation is not only tolerable but is desired. Some furnaces heat the work solely to promote oxidation. Furnaces designed for air operation are not completely gas-tight which results in somewhat lower constmction costs. There are no particular problems encountered in selecting the insulation systems because almost all refractory insulations are made up of oxides. Heating element materials are readily available for the common temperature ranges used with air atmospheres. 

The effects of surface emissivity are exaggerated in high-temperature applications, and particular attention should be paid to the selection of the type of surface of the insulation system. Low-emissivity surfaces such as bright polished aluminum reduce heat loss by inhibiting the radiation of heat from the surface to the surrounding ambient... 

While thermal insulations are selected first for their resistance to heal flow, their other properties need evaluation for each application. Hence there is no "best" insulation because a material well suited to one service may be poorly suited to another. Economics must be studied in detail because in some services the cost of a highly efficient material per unit of thickness may be overcome by additional thickness of a less efficient material, provided there is room for the grealet thickness. All properties of materials must he considered for each exposure, even within the same system. Recognize that when different materials are used or different parts nl insulation sv -.tents that arc close together, the probability of using the wrong material on a particular surface is increased appreciably. Unless there is specific reason for wide use ol multiple types of materials, it may be prudent to accept some compromises of properties. 

An insulation system is to be selected for a furnace wall at 1000°C using first a layer of mineral wool blocks followed by fiber-glass boards. The outside of the insulation is exposed to an environment with h = 15 W/m2 °C and = 40°C. Using the data of Table 2-1 calculate the thickness of each insulating material... 

Foam thermal insulation was selected for the cable pipe because of its low cost and high reliability, as demonstrated by its use in LNG piping systems. Possible degradation of its insulating quality could be caused by the infiltration of water... 

EXPERIMENTAL PERFORMANCE AND SELECTION OF CRYOGENIC ROCKET INSULATION SYSTEMS... 

Another apphcation of cured fluoroelastomer is a multi layer insulator system for electrical conductors. This system possesses an extruded crossUnked fluoroelastomer outer layer with the fluoropolymer selected from copolymer or terpolymer of ethylene and TFE. 

The end result of these waveshapes being appUed to the motor terminals is increased stress on the insulation system. Since these waveshapes do not exist in sinewave applications it is clear that their effect has not been considered in standard AC motor insulation systems. The motor insulation system must be capable of withstanding both the increased thermal stress as well as the capadtively coupled currents and voltage stresses. Appropriate selection of... 

Silicone foam thus formed has an open ceU stmcture and is a relatively poor insulating material. Cell size can be controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam char yields of >65% can be achieved. Because of its excellent dammabiUty characteristics, siUcone foam is used in building and constmction fire-stop systems and as pipe insulation in power plants. Typical physical properties of siUcone foam are Hsted in Table 10. 

In the preceding paragraphs we have analysed the behaviour and characteristics of a system when grounded or left isolated. The ground fault factor (GFF) plays a very significant role in the selection of insulation level (BIL) and its coordination with the different equipment connected on the system. The application of a particular method of grounding would thus depend upon... 

Arc suppression coil or ground fault neutralizer Ground fault factor (GFF) Magnitude of temporary overvoltages Insulation coordination Application of different types of grounding methods (for HT, HV and EHV systems) Important parameters for selecting a ground fault protection scheme... 

Molecular weight, effect on centrifugal sizing, 159 Mollier charts, 27 Monitoring system, 356 Motor, 146 enclosure, 260 equations, 267 insulation, 257 locked rotor torque, 270 selection, 270 service factor, 262 starting characteristics, 270 starting time, 273, 274 synchronous vs induction, 265 variable frequency drives, 27/, 280 voltage, 258 Motors... 

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