Mica paper

For large motors, the practice is to wind the stator with formed coils (Figure 9.2). The coils are pre-formed and cured before insertion into the stator slots. They are insulated with resin-rich glass and mica paper tapes. The process of impregnation is therefore termed resin-rich insulation. The completed formed wound stator is then heated to remove trapped moisture and finally impregnated in varnish class F or H as required, under vacuum and pressure. The stator is then cured in an oven as described above. The process of insulation and curing conforms to powerhouse insulation requirements. This practice facili-... 

A typical capacitor consists of a p iir of conduciois separated by a thin layer of a dielectric substance -that is. by an eleclrical insulator that contains essentially no mobile, currcnl-earryiiii , charged species. The sitnpicst capacitor consists of two sheets of metal foil separated by a thin filiii of a dielectiic such as iir. oil. plastic, mica, paper, ceramic, or metal oxide, hx-cef)l for air and mica capacitors, the two layers of U)il mid the insulator arc usuall> folded or rolled inio [Pg.35]

Z7. There are many different types of capacitors, includ-it ceramic, air, mica, paper, and electrolytic. Investi-... 

Dielectric materials vary by cost and the capacitance needed for a specific application. Glass, ceramic, and mica papers are high quality, low capacitance dielectrics with extremely high breakdown resistance. Conversely, metal-ized polymer foils such as polystyrene, polyethylene terephthalate (PET), and Teflon (PTFE) are single-piece dielectric films that offer better capacitor performance. In recent years, polymer foils have come to dominate the static capacitor market because they have better stability at high temperatures, can be manufactured at lower cost, and age better than dielectric papers. 

Electrical insulating tapes made from silicone elastomers or silicone-resin coated glasscloth or mica paper are also widely used. Polyester or polyimide tapes are also available with heat-resistant silicone pressure-sensitive adhesive coatings. 

Early capacitors were usually made with paper or mica. Paper was used for large capacitance values and mica was used for high-frequency capacitors. With the advent of commercial polymer film production, these increasingly available materials became popular as capacitor dielectrics. Polymer films are ideally suited for capacitor manufacture because they ... 

D 1677-62 Untreated mica paper used for electrical insulation sampling and testing... 

Crawford, S. C. and J. C. Hickle Electrical Quality Classification of the Suitability of Reconstituted Mica Paper for Use as Receiving Tube Spacers, in D. Slater (ed.), Advances in Electron Tube Techniques, Proc. 5th Nat. Conf., 1960, Pergamon Press, New York, 1961. 

Rutile bodies are used in either the pure form or with minor additions of various materials for capacitors (substitutes for mica, paper and electrolytics), temperature compensating (tc) capacitors, trimmer condensers, bypass condensers, filter and power circuits, and as fillers for resins and low melting glasses. 

Mica paper - Mica paper is a fabricated alternative to natural sheet and built-up mica products. Scrap mica is delaminated through a combination of thermal, chemical, and mechanical treatments. The mica pulp is then processed on a papermaking machine into a continuous, homogeneous sheet of imiform thickness. 

Some types of cables are designed to give continued service under fire conditions, so that services such as fire-detection systems and emergency lighting are maintained until evacuation is completed. Common approaches to the provision of such a cable include that of using silicone rubber, which burns to leave an insulating residue, or mica paper backed with woven glass fabric and bound in resin ( mica tape ) as at least one layer of the insulation. The behaviour of these materials at elevated temperatures is therefore of considerable interest. 

Figure 5.12 Deformation curves for glass-woven tape (1) and two different varieties of mica paper.

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