Properties power factor

Electrical. Glasses are used in the electrical and electronic industries as insulators, lamp envelopes, cathode ray tubes, and encapsulators and protectors for microcircuit components, etc. Besides their abiUty to seal to metals and other glasses and to hold a vacuum and resist chemical attack, their electrical properties can be tailored to meet a wide range of needs. Generally, a glass has a high electrical resistivity, a high resistance to dielectric breakdown, and a low power factor and dielectric loss. 

The most important electrical properties of insulation are dielectric strength, insulation resistance, dielectric constant, and power factor. Corona resistance, although not stricdy an electrical property, is usually considered also (10). 

Power factor, like the dielectric constant, is a property that represents a power loss that takes place when a wire insulation becomes the dielectric of a condenser because of a surrounding sheath or other conducting medium. 

Dielectric Constant, Power Factor and Structure 111 Table 6.1 Typical electrical properties of some selected plastics materials at 20°C... 

Antioxidants may be assessed in a variety of ways. For screening and for fundamental studies the induction period and rate of oxidation of petroleum fractions with and without antioxidants present provide useful model systems. Since the effect of oxidation differs from polymer to polymer it is important to evaluate the efficacy of the antioxidant with respect to some property seriously affected by oxidation. Thus for polyethylene it is common to study changes in flow properties and in power factor in polypropylene, flow properties and tendency to embrittlement in natural rubber vulcanisates, changes in tensile strength and tear strength. 

The chemical resistance of polyethylene is, to a large measure, that expected of an alkane. It is not chemically attacked by non-oxidising acids, alkalis and many aqueous solutions. Nitric acid oxidises the polymer, leading to a rise in power factor and to a deterioration in mechanical properties. As with the simple alkanes, halogens combine with the hydrocarbon by means of substitution mechanisms. 

The insulating properties of polyethylene compare favourably with those of any other dielectric material. As it is a non-polar material, properties such as power factor and dielectric constant are almost independent of temperature and frequency. Dielectric constant is linearly dependent on density and a reduction of density on heating leads to a small reduction in dielectric constant. Some typical data are given in Table 10.6. 

The electrical properties of polypropylene are very similar to those of high-density polyethylenes. In particular the power factor is critically dependent on the amount of catalyst residues in the polymer. Some typical properties are given in Table 11.3 but it should be noted that these properties are dependent on the antioxidant system employed as well as on the catalyst residues. 

Because the polymer is polar it does not have electrical insulation properties comparable with polyethylene. Since the polar groups are found in a side chain these are not frozen in at the Tg and so the polymer has a rather high dielectric constant and power factor at temperatures well below the Tg (see also Chapter 6). This side chain, however, appears to become relatively immobile at about 20°C, giving a secondary transition point below which electrical insulation properties are significantly improved. The increase in ductility above 40°C has also been associated with this transition, often referred to as the 3-transition. 

Where plastics are to be used for electrical applications, then electrical properties as well as mechanical and other properties need to be considered. Whilst properties such as resistivity, power factor and dielectric constant are important, they may not be all-important. For example, although polyamides and many thermosetting plastics may show only moderate values for the above properties, they have frequently been used successfully in low-frequency applications. Perhaps more important for many purposes are the tracking and arcing resistance, which are frequently poor with aromatic polymers. 

Oridation. This is caused by contact with oxidising acids, exposure to u-v, prolonged application of excessive heat, or exposure to weathering. It results in a deterioration of mechanical properties (embrittlement and possibly stress cracking), increase in power factor, and loss of clarity. It affects most thermoplastics to varying degrees, in particular polyolefins, PVC, nylons, and cellulose derivatives. 

Material response is typically studied using either direct (constant) applied voltage (DC) or alternating applied voltage (AC). The AC response as a function of frequency is characteristic of a material. In the future, such electric spectra may be used as a product identification tool, much like IR spectroscopy. Factors such as current strength, duration of measurement, specimen shape, temperature, and applied pressure affect the electric responses of materials. The response may be delayed because of a number of factors including the interaction between polymer chains, the presence within the chain of specific molecular groupings, and effects related to interactions in the specific atoms themselves. A number of properties, such as relaxation time, power loss, dissipation factor, and power factor are measures of this lag. The movement of dipoles (related to the dipole polarization (P) within a polymer can be divided into two types an orientation polarization (P ) and a dislocation or induced polarization. 

The electric properties of a material vary with the frequency of the applied current. The response of a polymer to an applied current is delayed because of a number of factors including the interaction between polymer chains, the presence within the chain of specific molecular groupings, and effects related to interactions within the specific atoms themselves. A number of parameters are employed as measures of this lag, such as relaxation time, power loss, dissipation factor, and power factor. 

Electrical properties such as high dielectric strength, very low power factor readings, low dielectric constant over a wide range of frequencies, and comparatively long period of arc resistance are outstanding characteristics. 

Most siloxane polymers are excellent insulators, and electrical properties relevant to this characteristic are also much studied. Examples are resistivity, dielectric constant, dielectric losses, dielectric strength (resistance to electrical breakdown), and power factors.16... 

Testing of polyurethanes for their electrical properties due to the voltages required must be carried out using properly designed equipment. The electrical tests that are normally carried out are resistivity, insulation resistance, electric strength, tracking resistance, power factor, and permittivity. 

In the equation, a key figure is the loss factor—the product of the dielectric constant and the power factor, and an inherent property of the material to be heated. Some materials (such as asbestos, polyethylene, and polypropylene) have low loss factors and in practice for industrial applications, regardless of... 

Major advantages Ease of fabrication, clarity with Dame retard ancy. moderate dissipation (power) factor Low shrinkage, excellent adhesion Good general properties, low cost... 

Within their temperature limitations, UFs have good electrical properties. They have high dielectric strength, high arc resistance, no tendency to track after arcing, and a low order power factor. Their... 

Properties Clear, very viscous, pale-yellow liquid. D 1.20 (20/20C), fp (sets to a glass at -10C), bp >300C, flash p >375F (190C), refr index 1.615 (25C). Combustible. Viscosity decreases very rapidly when heated has high volume resistivity, low power factor, unusually high dielectric constant. 

As the mouldings are polar, the electrical insulation properties are not outstanding but are adequate for many purposes. At 100°C a typical woodflour-phenolic moulding has a dielectric constant of 18 and a power factor of 0.7 at 800 Hz. 

Electrical Data. The electrical properties of cured specimens of the epoxy resin, containing various quaternary phosphonium compounds, were obtained on 2 in. diameter discs (0.125 in. to 0.25 in. thick) using standard procedures (ASTM D150-65T). In these tests, the power factor (100 x tan 6) and dielectric constant (e ) data were usually measured at 150 C (and a frequency of 60 Hz) on resin samples which had been cured for 16 h at 135 C + 5 h at 150 C. 

The temperature dependence of thermoelectric properties such as the Seebeck coefl dent, electrical resistivity and power factor for two kinds of Ge dopant levels were clarified to shift the temperature ofthemaximmn power factor due to the dopant levels and sintered condition. The power factor at the maximmn for the sinteredMn-Si element was obtained 1.05-l.lxlft (W/mK2) as the promising thermoelectric element for hi and middle temperature range. 

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