Current curves

Figure 1.5 Speed-torque and speed-current curves at the rated stator voltage...

This is a vital relationship, which reveals that during start-up and until such speed, the reactance of the motor windings / 2> the rotor current will also remain almost the same as the starting current and will fall only at near the rated speed. (Refer to the current curves in Figures 1.5(a) and (b)). The initial inrush current in a squirrel cage induction motor is very high. In a slip-ring motor, however, it can be controlled to a desired level. (Refer to Section 5.2.1.)... 

Current overshoot during changeover from Y to A, point, a, on Y current curve (Figure 4.. ))... 

The current curve becomes abed (Figure 4.5) and current overshoots from on to ob momentarily, which may exceed 14-20/ ... 

The current curve becomes ah h h c d (Figure 4.5). There is no current overshoot beyond the normal current in A... 

Figure 5.1 Operating region of torque and current curves...

The torque and current curves are as shown in Figure 5.4. Determine the external resistance required to achieve a starting torque of 200%. 

Once /3 is known, the resistance value for each step can be determined. In the above case, the slip corresponds to the slip at the operating point of the torque or current curve, where the desired torque or current /max occurs, This can be obtained from the torque and current curves available from the motor manufacturer (Figure 5.4). 

Approximate current curve during a soft start... 

Normal current curve Base or pedestal voltage... 

Figure 6.63 Motoring and generating torque curves for a 1500/1000 r.p.m. dual-speed motor (torque and current curves for generating region are drawn for only low-speed winding)...

Test for speed-torque and speed-current curves 11/257... 

In the lower part of Fig. 3-20 the types and approximate positions of defects can be recognized from the potential and pipe current curves. Only in the region of the protection station is an off potential more negative than achieved, as a result of the... 

The motor and gear combination must provide the proper input speed to the compressor. Therefore, speed selection should consider whctRei the 1,800 rpm, or the 1,200 rpm motor and the corresponding gear provides the more economical combination. Before selecting motor speed, motor characteristics should be obtained for both speeds. The speed-torque and speed-current curves, power factor and efficiency values should be compared and evaluated. The most important considerations in matching the motor to a compressor are ... 

Fig. 1.62 Potential/current curves for a metal polarised (a) cathodically and (b) anodically. The horizontal intercepts xy, x y, x"y" with AB and CB represent the local cell currents respectively, and yz, y z, y z" the externally applied currents (cathodic and anodic). In bimetallic corrosion yz, y z, etc. will be the galvanic current /gjjv, flowing from to (see...

The rate at which the net current is picked up or discharged will be proportional to the change in structure/soil potential along the unprotected structure and this is shown by the dotted curve PCG C P in Fig. 10.39. At points where current is picked up the potential change is negative and the natural rate of corrosion is reduced as shown by the dotted curve below XX. The structure/soil potential is made more positive where the interaction current is discharged and the rate of corrosion at such points is increased, as shown by the dotted curve above XX. The maximum positive structure/soil potential occurs where the gradient of the net current curve NGN is steepest, that is at points C and C on the potential curve PCG C P. ... 

Since the corrosion potential of a metal in a particular environment is a mixed potential — where the total anodic current is equal to the total cathodic current —the potentiostatic curve obtained by external polarisation will be influenced by the position of the local cathodic current curve. (Edeleanu and Mueller have discussed the details which must be considered in the analysis and interpretation of the curves.) For this reason, residual oxygen in the test solution can cause a departure from the usual curve in such a... 

Polarographic maxima. Current-voltage curves obtained with the dropping mercury cathode frequently exhibit pronounced maxima, which are reproducible and which can be usually eliminated by the addition of certain appropriate maximum suppressors . These maxima vary in shape from sharp peaks to rounded humps, which gradually decrease to the normal diffusion-current curve as the applied voltage is increased. A typical example is shown in Fig. 16.3. Curve A is that for copper ions in 0.1 M potassium hydrogencitrate solution, and curve B is the same polarogram in the presence of 0.005 per cent acid fuchsine solution. 

With a well-defined polarographic wave where the limiting current plateau is parallel to the residual current curve, the measurement of the diffusion current is relatively simple. In the exact procedure, illustrated in Fig. 16.6(a), the actual... 

It is simpler, though less exact, to apply the extrapolation method. The part of the residual current curve preceding the initial rise of the wave is extrapolated a line parallel to it is drawn through the diffusion current plateau as shown in Fig. 16.6(h). For succeeding waves, the diffusion current plateau of the preceding wave is used as a pseudo-residual current curve. 

FIGURE 3-3 Variation of the charging (curve A) and diffusion currents (curves B) dining the lifetime of a drop. 

FIGURE 3-9 Square-wave voltammograms for reversible electron transfer. Curve A forward current. Curve B reverse current. Curve C net current. (Reproduced with permission from reference 9.)... 

The polarographic wave of TBA or TPenA is observed at potentials where the polarographic current (curve 1) due to the eleetron transfer appears, whieh suggests that the coupling of the transfer of TBA" " or TPenA with the electron transfer occurs when W containing NADH and TBA or TPenA is shaken with DCE containing CQ [44]. Since... 

Theoretically, at a low Uappl the counteraction would be expected to result in full polarization of the electrodes, i.e., would become equal to Eappl, so no current will be passed however, the actual pc,2 at the electrode surface is continuously diminished by diffusion of the Cl2 gas into the solution and so there results a residual current, i = (2 appl - E fR. The amount of the latter increases more or less gradually with increasing Uappl, because the actual pC 2 increases until it finally becomes 1 atm, where Cl2 gas starts to escape from the solution. In the meantime, the anode has been completely covered with Zn metal, so that [Zn] has become unity. In fact, E has now attained a constant maximum value, the so-called decomposition potential, where electrolysis really breaks through. Any further increase in app) would, according to first expectations, cause a linear current increase, i = ( app, - Edecomp )IR. However, Fig. 3.2 shows that the experimental current curve deviates more and... 

In voltammetry as an analytical method based on measurement of the voltage-current curve we can distinguish between techniques with non-stationary and with stationary electrodes. Within the first group the technique at the dropping mercury electrode (dme), the so-called polarography, is by far the most important within the second group it is of particular significance to state whether and when the analyte is stirred. 

Fig. 1. Experimental limiting-current curve for copper deposition from an acidified cupric solution. [From Hickman (H3).]...

Fig. 3. (a) Typical galvanostatic limiting-current curve for copper deposition at a copper disk in acidified CuS04 solution. The circles indicate the experimental curve. The solid curves were calculated using kinetic parameters as indicated, (b) Typical galvanostatic limiting current curve for ferricyanide reduction at a nickel electrode in equimolar ferri ferrocyanide solution with excess NaOH. [From Selman (S8).]... 

It is clear from the calculated limiting-current curves in Fig. 3a that the plateau of the copper deposition reaction at a moderate limiting-current level like 50 mA cm 2 is narrowed drastically by the surface overpotential. On the other hand, the surface overpotential is small for reduction of ferri-cyanide ion at a nickel or platinum electrode (Fig. 3b). At noble-metal electrodes in well-supported solutions, the exchange current density appears to be well above 0.5 A/cm2 (Tla, S20b, D6b, A3e). At various types of carbon, the exchange current density is appreciably smaller (Tla, S17a, S17b). 

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