Short-time factors

In most applications, a bar primary CT is generally used and a normal CT may be suitable. But for too small ratings, where the use of a wound primary CT is imperative, short-circuit effects must be considered, except the CTs for an LT system, where the fault level for such small ratings may be very low and may not matter (Section 13.4.1(5)). For applications on an HT system, where a wound primary CT is imperative, choice of a CT from standard wound primary CTs may still be possible, meeting the minimum requirements of class of accuracy, VA burden and short-time rating. lEC 60044-1 indicates for measuring and protection CTs the maximum short-time factors (STF) that can be obtained economically for a normal wound primary CT where... 

Table 15.11 Maximum short-time factors obtainable economically corresponding to rated output, accuracy class, accuracy limit factor and rated short-time for wound primary current transformers...

Usually, diffusivity and kinematic viscosity are given properties of the feed. Geometiy in an experiment is fixed, thus d and averaged I are constant. Even if values vary somewhat, their presence in the equations as factors with fractional exponents dampens their numerical change. For a continuous steady-state experiment, and even for a batch experiment over a short time, a very useful equation comes from taking the logarithm of either Eq. (22-86) or (22-89) then the partial derivative ... 

Metals Successful applications of metals in high-temperature process service depend on an appreciation of certain engineering factors. The important alloys for service up to I,I00°C (2,000°F) are shown in Table 28-35. Among the most important properties are creep, rupture, and short-time strengths (see Figs. 28-23 and 28-24). Creep relates initially applied stress to rate of plastic flow. Stress... 

Prospective short-circuit or short-time current Asc kA(r.m.s.) (symmetrical breaking current) Factor of asymmetry to obtain the peak short circuit or making current Co s (p... 

Duty cycles Continuous duty (CMR) (S ) Periodic duties Factor of inertia (FI) Pleating and cooling characteristic curves Drawing the thermal curves Rating of short motors Equivalent output of short time duties Shock loading and use of a flywheel... 

The actual mass flow rates and speeds are corrected by factor ( /0/ ) and (l/ /0) respectively, reflecting variations in inlet temperature and pressure. The surge line joins different speed lines where the compressor s operation becomes unstable. A compressor is in surge when the main flow through a compressor reverses direction for short time intervals, during which the back... 

Pressure Vessels. Refineries have many pressure vessels, e.g., hydrocracker reactors, cokers, and catalytic cracking regenerators, that operate within the creep range, i.e., above 650°F. However, the phenomenon of creep does not become an important factor until temperatures are over 800°F. Below this temperature, the design stresses are usually based on the short-time, elevated temperature, tensile test. 

Since the adsorbent bed must be heated in a relatively short time to reactivation temperature, it is necessary that the reactivation steam rate calculation is increased by some factor that will correct for the nonsteady-state heat transfer. During the steaming period, condensation and adsorption will take place in the adsorbent bed, increasing the moisture content of the adsorbent. A certain portion of the adsorbate... 

Although equations (2.112), (2.113) and (2.115) can be useful they must not be used indiscriminately. For example, they are seldom accurate at short times but this is not a major worry since such short-time failures are usually not of practical interest. At long times there can also be inaccurate due to the embrittlement problem referred to earlier. In practice therefore it is generally advisable to use the equations in combination with safety factors as recommended by the appropriate National Standard. 

Dynamic information such as reorientational correlation functions and diffusion constants for the ions can readily be obtained. Collective properties such as viscosity can also be calculated in principle, but it is difficult to obtain accurate results in reasonable simulation times. Single-particle properties such as diffusion constants can be determined more easily from simulations. Figure 4.3-4 shows the mean square displacements of cations and anions in dimethylimidazolium chloride at 400 K. The rapid rise at short times is due to rattling of the ions in the cages of neighbors. The amplitude of this motion is about 0.5 A. After a few picoseconds the mean square displacement in all three directions is a linear function of time and the slope of this portion of the curve gives the diffusion constant. These diffusion constants are about a factor of 10 lower than those in normal molecular liquids at room temperature. 

The mechanical behavior of plastics on time-dependent applied loading can cause different important effects on materials viscoelasticity. Loads applied for short times and at normal rates (Chapter 2) causes material response that is essentially elastic in character. However, under sustained load plastics, particularly TPs, tend to creep, a factor that is included in the design analysis. 

The complexity of the problems associated with future food packaging can be seen from these examples. We have focused on only one factor in one segment of the food industry—the effect of change in solid waste disposal. The present uncertainties in technical and political aspects of the disposal problem prevent a definite decision as to whether packaging changes should be made. All the industry can do at present is prepare itself for a possible major shift that would have to be made in a short time. 

Effect of UV on Productivity of the Southern Ocean. Has ozone depletion over Antarctica affected the productivity of the Southern Ocean There is no easy answer. First, one has to take into account the fact that the drastic decrease of ozone over Antarctica has been reported as recently as 1976, a relatively short time in the evolution of the organisms to develop mechanisms to cope with elevated UV. One of the most vexing problems in studying the effects of UV radiation on productivity, is a dearth of historical data on the level of UV. Without these baselines, normal fluctuations could easily be interpreted as decline in productivity. Second, there is a host of biotic and abiotic factors that play significant roles in governing the productivity of the Southern Ocean (40). Ultraviolet radiation is but one more complicating factor to be considered in an already stressful environment. 

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