Loss factor

Tetralluoroethylene polymer has the lowest coefficient of friction of any solid. It has remarkable chemical resistance and a very low brittleness temperature ( — 100°C). Its dielectric constant and loss factor are low and stable across a broad temperature and frequency range. Its impact strength is high. 

The time-temperature superpositioning principle was applied f to the maximum in dielectric loss factors measured on poly(vinyl acetate). Data collected at different temperatures were shifted to match at Tg = 28 C. The shift factors for the frequency (in hertz) at the maximum were found to obey the WLF equation in the following form log co + 6.9 = [ 19.6(T -28)]/[42 (T - 28)]. Estimate the fractional free volume at Tg and a. for the free volume from these data. Recalling from Chap. 3 that the loss factor for the mechanical properties occurs at cor = 1, estimate the relaxation time for poly(vinyl acetate) at 40 and 28.5 C. 

G1 as s CO de b Thei mal stress resist ance °c Strain, °C Anne alia °C Soften in °c Workin °C Knoo P hardn ess, HKio 0 Den sity, g/c 3 m Youn g s mod ulus, GPa Poiss on s ratio 25° C 25 0° C 350 °C Powe r factor, % Diele ctric const ant Loss factor, % Refrac tive index... 

Dioxetanones decompose near or below room temperature to aldehydes or ketones (56). The decomposition reactions are weakly chemiluminescent Qc ca 10 ein/mol) because the products are poorly fluorescent. However, addition of 10 M mbrene provides 2iQc ca 10 ein/mol, and 2iQc on the order of was calculated at mbrene concentrations above 10 M after correcting for yield loss factors (57). The decomposition rates are first order ia... 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

Multiphoton processes are also undoubtedly involved in the photodegradation of polymers in intense laser fields, eg, using excimer lasers (13). Moreover, multiphoton excitation during pumping can become a significant loss factor in operation of dye lasers (26,27). The photochemically reactive species may or may not be capable of absorption of the individual photons which cooperate to produce multiphoton excitation, but must be capable of utilising a quantum of energy equal to that of the combined photons. Multiphoton excitation thus may be viewed as an exception to the Bunsen-Roscoe law. 

Sihcone fluids have good dielectric properties, loss factor, specific resistance, and dielectric strength at normal operating conditions, and the properties vary only slightly with temperature (59,328,350). The properties in combination with relatively low flammabiUty have led to the use of siUcones in transformers and other large electrical appHcations (351). The dielectric constant of a 1000-cSt oil is 2.8 at 30°C and 2.6 at 100°C. The loss factor is low,... 

A high temperature thermocouple uses sihcon carbide (146). It is also used in lightning arrestors to protect high tension power lines, and in high loss factor microwave attenuators (147). 

The observed dielectric constant M and the dielectric loss factor k = k tan S are defined by the charge displacement characteristics of the ceramic ie, the movement of charged species within the material in response to the appHed electric field. Discussion of polarization mechanisms is available (1). 

Ejftciency Factors Representative efficiency data for boilers, pyrolytic reacdors, gas turbines, steam-turbine-generator combinations, electric generators, and related plant use and loss factors are... 

TABLE 25-67 Typical Thermal Efficiency and Plant Use and Loss Factors for Individual Components and Processes Used for Recovery of Energy from Solid Wastes... 

Theory of dielectric loss factor or dissipation factor (tan 5) 9/227... 

By monitoring the insulation condition of the windings during maintenance, at least once a year, which can be carried out by measuring (a) the polarization index (Section 9.5.3) and (b) the dielectric loss factor, tan S (Section 9.6) and making up the insulation as in Section 9.5.2, when the condition of the insulation is acceptable and only its level is less than permissible. 

The tests for insulation resistance and dielectric loss factor should, however, be carried out on a completed machine also with formed coils to establish reference data for field tests, as noted in Section 9.6. However, these tests on a completed machine with formed coils do not monitor the process quality of insulation. 

Table 11.5 Highest permissible values of loss tangent or dielectric loss factor at rated voltages not exceeding 11 kV...

For lower voltage systems, say. 2.5 to lU kV, measurement of dielectric loss factor tan 5. along similar lines, to those recommended... 

Conangla, A. and White, H.E., Isolated-phase bus enclosure loss factors , Trans. IEEE, 87, August, 1622-1628 (1968). 

Figure 6.3. The variation of dielectric constant e and the loss factor e" with frequency. (After Frith and Tucketl, reproduced by permission of Longmans, Green and Co. Ltd.)...

---