## 8 Application of CGRR Index in Power System Operating Decisions
### System Operation Using CGRR Criterion
The change in loading to satisfy the system change is first determined using an economic load dispatch. The CGRR for the new economic load dispatch is evaluated and compared with the accepted criterion, as shown in \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Units**} & **MCR** & **Ramping Capability** & \multicolumn{2}{c}{**ELD**} & \multicolumn{2}{c}{**Re-Dispatch**} \\ \cline{3-7}  & **(MW)** & **(MW)** & **Loading (MW)** & **RM (MW)** & **Loading (MW)** & **RM (MW)** \\ \hline
1-A & 50 & 50 & 50 & 0 & 50 & 0 \\
2-A & 50 & 50 & 50 & 0 & 50 & 0 \\
3-A & 50 & 50 & 50 & 0 & 50 & 0 \\
4-A & 50 & 50 & 50 & 0 & 50 & 0 \\
5 & 400 & 0 & 400 & 0 & 400 & 0 \\
6 & 400 & 0 & 400 & 0 & 400 & 0 \\
7-A & 350 & 90 & 302 & 48 & 276 & 74 \\
8-B & 197 & 60 & 80 & 60 & 104 & 60 \\
9-B & 197 & 60 & 80 & 60 & 104 & 60 \\
10-B & 197 & 60 & 80 & 60 & 104 & 60 \\
11-A & 155 & 50 & 151 & 4 & 135 & 19 \\
12-A & 155 & 50 & 151 & 4 & 136 & 19 \\
13-A & 155 & 50 & 151 & 4 & 136 & 19 \\ \hline Total & 2406 & 620 & 1995 & 240 & 1995 & 311 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Example of economic re-dispatch in the IEEE-RTS operating schedule to meet CGRR criterion. Figure 4: Algorithm for implementing CGRR criterion in operating decisions. Figure 4. This new dispatch action is taken if the CGRR criterion is satisfied. If the criterion is not met, the economic dispatch is modified by transferring the load from the class A units to the class B units one step at a time in a recursive approach until the CGRR criterion is satisfied. A decision is then taken to implement the resulting load dispatch that meets the risk criterion. If the system does not have adequate regulate the margin to meet the CGRR criterion, the commitment of the next available standby unit with the lowest incremental operating cost is considered as the additional generating unit in the CGRR evaluation, and the load dispatch that results in an acceptable CGRR value is determined by repeating the above described process, as shown in the algorithm. A decision is then taken to commit the selected additional unit. The CGRR evaluation and the implementation decision proceed continuously in time chronology in order to consistently maintain the CGRR within the acceptable criterion value. The algorithm in Figure 4 is further illustrated with an example of an IEEE-RTS operating condition, in which 13 generating units are committed from the priority loading order. The total committed generation capacity is 2406 MW. In this example, the failure rates of the individual generating units are assumed to be 1.5 times that of their original values. It is assumed that the short-term system load forecast is 2006 MW in this example. The economic load dispatch (ELD) of the committed 13 units to meet the forecast load is shown in the fourth column of Table 8. The total regulating margin is 230 MW, and the resulting CGRR is 0.004062. These results are shown in the first row of Table 9. The operating risk is unacceptable as it is well above the criterion value of 0.002698. Following the algorithm in Figure 4, a re-dispatch is considered, since the total regulating margin can be increased by economic load transfer from the class A units 11, 12, and 13 to class B units 7, 8, 9, and 10. The economic re-patch to lower the operating risk is shown in the sixth column of Table 8. The CGRR result and the total regulating margin is shown in the second row of Table 9. The new CGRR is 0.002740, which is also unacceptable. The regulating margin is increased by 168 MW and cannot be further increased due to loading constraints of the committed units. In order to further decrease the CGRR, the commitment of an additional generating unit is considered, as shown in the algorithm of Figure 4. The eighth column in Table 8 shows the economic load dispatch (ELD) of the committed units, considering the addition of a 155 MW unit that has a failure rate of 9.13 occurrences per year.