Capacitors and insulators

is nothing but the square of the refractive index) together with tan 0 of a number of ceramics. 

In general, dielectrics are grouped into three classes  

Class 1 dielectrics include ceramics with relatively low and medium dielectric constants and dissipation factors of less than 0.003. The low range covers / static = 5 to 15, and the medium /Tstatic range is 15 to 500. 

Class II dielectrics are high-permittivity ceramics based on ferroelectrics (see Chap. 15) and have values of k between 2000 and 20,000. 

Class III dielectrics (not discussed here) contain a conductive phase that effectively reduces the thickness of the dielectric and results in very high capacitances. Their breakdown voltages are quite low, however. 

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Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

All electrical equipment are designed for a specific BIL, as indicated in Tables 11.6, 13.2, 14.1, and 32.1(A) for motors, switchgears and bus systems respectively, and Tables 13.2 and 13.3 for the main power system (line clearances and insulators). If the actual severity of a prospective surge, i.e. its amplitude and/or rise time or both, is expected to be higher than these levels (higher amplitude and lower rise time) the same must be damped to a safe level, with the use of surge arresters, surge capacitors or both as discussed later. 

We provide in Table 25.1 a brief comparison of the different types of dielectrics in use for impregnation and insulation while forming capacitor elements. The table will also help make a proper choice of the dielectric and the type of capacitors for a particular application. 

See also Capacitors and Ultracapacitors Electric Motor Systems Electric Power, Generation of Electric Power, System Protection, Control, and Monitoring ol Electric Power, System Reliability and Electric Power Substations Environmental Problems and Energy Use Insulation T ransformers. 

Aluminium is widely applied for decorative and protective requirements, while cadmium , zinc and titanium have been applied to ferrous materials chiefly for their protective value. The method finds particular application in the plating of high-tensile steels used in aviation and rocketry, car fittings and lamp reflectors, and gramophone record master discs, as well as in the preparation of specimens for electron microscopy and in rendering insulated surfaces electrically conducting, e.g. metallising of capacitors and resistors. 

The dielectric constant is the ratio of the capacity of a condenser made with a particular dielectric to the capacity of the same condenser with air as the dielectric. For a material used to support and insulate components of an electrical network from each other and ground, it is generally desirable to have a low level of dielectric constant. For a material to function as the dielectric of a capacitor, on the other hand, it is desirable to have a high value of dielectric constant, so that the capacitor may be physically as small as possible. 

When selecting polymers for use as insulators, in capacitors, and other electrical applications, we must consider factors other than their interaction with electric fields. The following examples illustrate some of the other factors that we must consider. 

There has been a tremendous interest in polymers since World War 11. In the US, consumption was 18 million metric tons in 1974, 25.7 million metric tons in 1984, and 41.3 million metric tons in 1994 [1]. Polymer production has increased from essentially zero at the end the World War II to about 101 million metric tons worldwide in 1993 [2] and 241 million metric tons in 2006 [3]. The reason for this increase is quite simple. Synthetic polymers are numerous in structure and are very diverse in their structure-property relationships. Polymers are used extensively in electrical applications, including insulators, capacitors, and conductors. They are also used in many optical applications, the biochemical industry, structural applications, packaging, and they are used extensively as thermal insulation [4]. 

The metal has very little commercial use. In elemental form it is a laser source, a portable x-ray source, and as a dopant in garnets. When added to stainless steel, it improves grain refinement, strength, and other properties. Some other applications, particularly in oxides mixed with other rare earths, are as carbon rods for industrial hghting, in titanate insulated capacitors, and as additives to glass. The radioactive isotope ytterbium-169 is used in portable devices to examine defects in thin steel and aluminum. The metal and its compounds are used in fundamental research. 

Since the capacitor, Schottky diode, and transistor all contain an insulating layer under the catalytic metal, they are all referred to in this chapter as field-effect devices. In published literature, the capacitor and diode SiC devices are often referred to as MISiC devices, and the transistor as an MISiC-FET device. 

The success of CD CdS in photovoltaic cells has driven related research with potential applications in other semiconductor devices. Since the CD process seems to play a role in the favorable properties of the CdS windows by decreasing interface recombination, studies of its passivation properties on other interfaces and surfaces have been carried out, with considerable success. For example, when a very thin film (ca. 6 nm) was deposited between InP and SiOi, the resulting reduction of the interface state density led to improved electrical properties of metal-insulator-semiconductor capacitors and field effect transistors (FETs)... 

Part I is focused on capacitors, providing the oportunity to introduce the many important ideas relating to their performance and, indeed, to the wider application of dielectrics and insulators. Part II is concerned with the important ceramic types and their applications. 

Ceramic dielectrics and insulators cover a wide range of properties, from steatite with a relative permittivity of 6 to complex ferroelectric compositions with relative permittivities exceeding 20000. For the purposes of this discussion insulators will be classed with low permittivity dielectrics, although their dielectric loss may be too high for use in capacitors. Reference should be made to Table 5.10 and Fig. 5.40. 

PCBs, originally called chlorinated diphenyls, were commercially produced as complex mixtures containing multiple congeners at different degrees of chlorination. In the United States, commercial production of PCBs started in 1929. Manufacturing levels increased in response to the electrical industry s need for a safer (than flammable mineral oil) cooling and insulating fluid for industrial transformers and capacitors. 

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