Voltage Profiling

Fig. 3. CeU voltage profiles as a function of discharge capacity for rechargeable "AA" ceUs A, Li ion B, Li—SO2 C, Li—Mn02 L), Li—TiS2 E, Li—M0S2 F,...

Figure 24.9 shows a typical output characteristic or reactive capability curve of a generator, illustrating the stability levels of the machine under different conditions of operation. The machine must operate within these levels and the voltage profile within the specified voltage limits, as noted in Table 24.3. 

To apply the corrective measures to limit the Ferranti effect it is essential to first study its over voltage (OV) status at the far end of the line. Consider the earlier system TZ of 400 kV 50 Hz and draw a voltage profile as illustrated in Figure 24.17, for the voltages worked out as in equation (24.7), at different lengths of the line. The voltages, for the sake of simplicity, are also shown in Table 24.4. 

Figure 24.17 Voltage profile of a 400 kV/400 km radial line on a no-load illustrating the Ferranti effect...

The element Pg/sin B can be considered as the steady-state stability limit of the line, say P ax- I tie length compensation can improve the voltage profile and hence the power transfer capability of the line as follows. 

Curve I without any compensation, the voltage profile sags on small load variations and is not capable of transferring even a natural load. 

Curve 2 with partial compensation, the voltage profile improves and the line is able to transfer more load than above, but less than its natural loading. Voltage still sags but the swing is more tolerable. 

Curve 3 The line is fully compensated. The voltage profile tends to be flat and the line is capable of transferring even more than the natural load without an appreciable sag in the voltage profile. 

When the line is compensated, and a near-flat voltage profile can be ensured so that during all such disturbances the receiving-end voltage will stay within permissible limits, the load angle can be raised to 45-60° to achieve a high power transfer. 

At unity p.f. the voltage variation and hence the regulation is the least and maintains a near-flat voltage profile. This is the best condition to provide the highest level of system stability from a voltage point of view. 

A line can be theoretically loaded up to these levels. But at these levels, during a load variation, the far-end voltage may swing far beyond the desirable limits of 5% and the system may not remain stable. With the use of reactive control it is possible to transfer power at the optimum level (Pnias) hd yet maintain the far-end (or midpoint in symmetrical lines) voltage near to and also to have a near-flat voltage profile. 

Reactive control can alter the line length ( f LC) to the level at which the system will have the least possible swings. It is evident from these curves that an uncompensated line of a much shorter length may not be able, to transfer even its natural load (Pq) successfully. This is due to the steeply drooping characteristics of the voltage profile at about this load point, which may subject the... 

Fig. 3. Second cycle voltage profiles of carbons representative of regions (I), (2), and (3). a) JMI synthetic graphite, b) Crowley petroleum pitch heated to 550°C, and c) a resole resin heated to 1000°C.

Figure 7 shows voltage profiles, for the second cycle of most of the graphitic carbon samples listed in Table 1. The curves have been sequentially offset by 0.1 V for clarity. Most striking is a reduction of the maximum reversible capacity, or Q ,, (<2 =372-x ,3,), as P increases. 

It is not surprising that it is difficult to insert lithium between parallel layers which are randomly stacked. When lithium intercalates between AB stacked layers, a shift to AA stacking occurs [26]. It is likely that the turbostratically stacked layers are pinned by defects (which can only be removed near 2300°C ) preventing the rotation or translation to AA stacking. Thus, we can understand why varies as 372(1-P), the fraction of layers with AB registered stacking. More studies of the details of the voltage profiles in Fig. 7 can be found elsewhere [6,7,27]. 

Figure 25 shows the second cycle for the Br-series carbonaceous materials. The voltage profiles of the Ar and Cr-series samples were similar to those of the Br-... 

The current-voltage profile of rectifying junctions is strongly asymmetrical. The reason for this can be explained with the aid of a simple band diagram shown in Figure 14-2. 

There are distinct differences in the electrochemical behavior of lithium cells constructed with /1-Mn02 electrodes prepared by acid treatment and those containing Li[Mn2]04 electrodes [120].Cells with A-Mn02 electrodes show an essentially featureless voltage profile at 4V on the initial discharge on subsequent cycling, the cells show a profile more consistent with that expected from an Li[Mn2]04 electrode. 

Figure 9 shows voltage profiles of the initial and modified Graphite-type materials at first charge (A) and subsequent discharge-charge (B) processes. 

Figure 9. Voltage profiles of Hohsen Graphite-Type Material modified with the Co-Ni complex A -first charge, part of it is enlarged in the insert ...

Figure 6. Voltage profiles of lithium cells with (a) uncoated MAG-10 graphite and (b) 11.7wt% Cu-graphite (MAG-10) electrodes in 30% PC blended electrolyte and at 50°C. 

Figure 9. Typical discharge (lithiation) voltage profile of the Li/11.7%Cu-graphite cell at 50 °C in 1 1 EC DEC (1 MLiPF6 LP-40). Inset is an expanded region showing the voltage relaxation change during current interruption at about 0.08 V of the Li/11,7%Cu-graphite...

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