Current Symmetrical

We assume that A is a symmetric and positive semi-definite matrix. The case of interest is when the largest eigenvalue of A is significantly larger than the norm of the derivative of the nonlinear force f. A may be a constant matrix, or else A = A(y) is assumed to be slowly changing along solution trajectories, in which case A will be evaluated at the current averaged position in the numerical schemes below. In the standard Verlet scheme, which yields approximations y to y nAt) via... 

As noted above, one of the goals of NAMD 2 is to take advantage of clusters of symmetric multiprocessor workstations and other non-uniform memory access platforms. This can be achieved in the current design by allowing multiple compute objects to run concurrently on different processors via kernel-level threads. Because compute objects interact in a controlled manner with patches, access controls need only be applied to a small number of structures such as force and energy accumulators. A shared memory environment will therefore contribute almost no parallel overhead and generate communication equal to that of a single-processor node. 

Naturally occurring porphyrins are usually symmetrically substituted about the 15-methine bridge. These porphyrins can be synthesized by the condensation of two dipyrroiic intermediates. Typical dipyrroiic intermediates in current use arc the dipyrromethanes and the dipyrromethenes. Both methods will shortly be described. This again is a highly specialized... 

Because there are two changes ia material composition near the active region, this represents a double heterojunction. Also shown ia Figure 12 is a stripe geometry that confines the current ia the direction parallel to the length of the junction. This further reduces the power threshold and makes the diffraction-limited spreading of the beam more symmetric. The stripe is often defined by implantation of protons, which reduces the electrical conductivity ia the implanted regions. Many different stmctures for semiconductor diode lasers have been developed. 

Ion Channels. The excitable cell maintains an asymmetric distribution across both the plasma membrane, defining the extracellular and intracellular environments, as well as the intracellular membranes which define the cellular organelles. This maintained a symmetric distribution of ions serves two principal objectives. It contributes to the generation and maintenance of a potential gradient and the subsequent generation of electrical currents following appropriate stimulation. Moreover, it permits the ions themselves to serve as cellular messengers to link membrane excitation and cellular... 

The magnitudes of symmetrical and non-symmetrical fault currents, under different conditions of fault and configurations of faulty circuits, can be determined from Table 13.5, where Z] = Positive phase sequence impedance, measured under symmetrical load conditions. The following values may be considered ... 

Therefore, the level of phase-to-phase asymmetrical faults will he generally of the same order as the three-phase symmetrical faults. The ground faults, however, will he higher than the symmetrical faults. Special care therefore needs he taken while grounding a generator, when they are solidly grounded, particularly to limit the ground fault currents See also Section 20.10.1. 

This is a simple calculation to determine the maximum symmetrical fault level of a system, to select the type of equipment, devices and bus system etc. But to decide on a realistic protective scheme, the asymmetrical value of the fault current must be estimated by including all the likely impedances of the circuit. 

These reactances are measured by creating a fault, similar to the method discussed in Section 14.3.6. The only difference now is that the fault is created in any of the phases at an instant, when the applied voltage in that phase is at its peak, i.e. at Vni- so that the d.c. component of the short-circuit current is zero and the waveform is symmetrical about its axis, as shown in Figure 13.19,... 

A fault current on a power system is normally asymmetrical as discussed next, and is composed of a symmetrical a.c. component /sar.m.s.) nd an asymmetrical sub-transient d.c. component (Figure 14.5). The forces arising out of /jc aie referred to as electromagnetic and... 

Symmetrical Minimum intermitting momentary current current peak for... 

The peak value of a fault current will depend upon the content of the d.c. component. The d.c. component will depend upon the p.f. of the faulty circuit and the instant at which the short-circuit commences on the current wave. (Refer to Figure 13.27, illustrating the variation in asymmetry with the p.f. of the faulty circuit. For ease of application, it is represented as a certain multiple of the r.m.s. value of the symmetrical fault current /sc )... 

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... 

A current wave propagating symmetrically about its zero axis, i.e. when the envelopes of the peaks of the current wave are symmetrical about its zero axis, is termed symmetrical (Figure 13.24) and a wave unable to maintain this symmetry is termed asymmetrical (Figure 13.25). 

When the short-circuit occurs at a current zero, i.e., when the applied voltage is almost at its peak, the voltage and current waves will follow Figure 13.19, the cuiTent lagging the voltage by almost 84°. The current will now be almost symmetrical. 

The generation of an asymmetrical current on an a.c. system, leads to the inference that a short-circuit condition will give rise to a d.c. component due to a shift in its zero axis. During the sub-transient state the value of the asymmetrical current will be the phasor sum of the symmetrical /sc and the asymmetrical current components. For details refer to Section 14.3.6. 

This test is conducted to verify the suitability of the equipment to withstand a prospective short-circuit current that may develop on a fault. It may also be termed the steady slate symmetrical fault current or the short-time (withstand current) rating of the equipment. When the equipment is an interrupting device, it is referred to as its symmetrical breaking current. 

This is also known as the asymmetrical breaking current and tends to become the symmetrical r.m.s. value of the fault current / c after almost four cycles from the instant of fault initiation, as discussed in Section 13.4.1(8). 

The d.c. component, /j ., at any instant should be a niininiuni of 50% that of the corresponding peak value of the a.c. component of the symmetrical fault current /.,c, /.,ci. /jctri. at any instant, during the period of the short-circuit condition, /jc should bo S 0..S V2 /jc- Otherwise the asymmetry may be ignored, being insignificant. 

This is the steady-state symmetrical fault current, which the faulty circuit may almost achieve in about three or four cycles from commencement of the short-circuit condition at point Oi (Figure 14.5) and which the interrupting device should be able to break successfully. 

The instant (sub-transient) fault current, /jjgf, through a generator in a symmetrical three-phase system, irrespective of the condition of neutral as defined in Table 13.9 will be... 

Generalizing the above, the symmetrical fault current, when n number of machine.s are operating in parallel. 

This is less than the corresponding symmetrical fault current of 34.2u and incidentally equal to the ground fault current when only one machine is grounded at a time. By this method, the ground fault current can be controlled to any desired level. We have considered a resistance with a view to improving the p.f. of the fault current and thus, making it easier to interrupt. 

Iq = jiiaximum ground fault current /,j = symmetrical ground fault current D, = decrement factor... 

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