# Power System Reliability Assessment Considering Coal-Fired Unit Peaking Characteristics
## 6 Case Study
### Impact of Different Peak Shaving Schemes  
This section analyzes the impact of unit peak shaving operation on the system under different peak shaving schemes. The range of the unit's load change rate is set from 1% to 5%, and the peak shaving depth is set to 90%, 80%, 70%, 60%, 50%, and 40%. Based on the integration of a 300 MW wind turbine, different peak shaving schemes are obtained by pairing the various peak shaving parameters. PPS is then conducted to study the system's reliability, economic performance, and renewable energy absorption capacity. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Number** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **LOLP** & **EENS** \\ \hline Method 1 (GWh) & 1.15 & 0.89 & 2594.59 & 680.45 & 18.64 & 3002.4 & 333.29 & 2521.74 & 6142.75 & 0.011 & 1.18 \\ Method 2 (GWh) & 1.15 & 0.89 & 2594.59 & 680.45 & 18.64 & 3002.4 & 333.29 & 2521.74 & 6142.75 & 0.011 & 1.18 \\ Method 3 (GWh) & 4.90 & 5.45 & 2594.59 & 655.93 & 46.98 & 2929.28 & 374.4 & 2521.65 & 6142.74 & 0.0158 & 20.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of random production simulation results using different methods. Analysis of Simulation Results Based on LOLP, Expected Wind Curtailment, Start-Stop Counts, and Generation Costs: As shown in Figure 6, under varying ramp rates, the LOLP increases with deeper peak shaving depths. This is due to the fact that as the peak shaving depth increases, the units operate outside of their design conditions, significantly affecting their reliability. Additionally, it can be observed that when the ramp rate is between 2% and 3%, the LOLP decreases. This is because an increase in ramp rate allows the units to respond to load demand more promptly while ensuring reliable operation. However, as the ramp rate rises from 4% to 5%, the LOLP increases again. The larger fluctuations in output at higher ramp rates can severely compromise the unit's operational reliability, reduce its lifespan, and consequently affect the overall system's reliability. As shown in Figure 7, the expected wind curtailment decreases with an increase in peak shaving depth. This is because a deeper peak shaving depth creates more space for wind power absorption, effectively facilitating the integration of renewable energy. It is also observed that when the ramp rate is between 2% and 3%, compared to 1%, the wind curtailment is relatively alleviated. The flexibility in the ramping capability of the units is an important factor in ensuring wind power absorption. However, when the ramp rate is set to 4% to 5%, the expected wind curtailment increases again. The severe fluctuations in load demand at higher ramp rates significantly impact the unit's thermal operation, thereby hindering the absorption of wind power. With an increase in peak shaving depth, the start-stop frequency of the units also rises. The larger the peak shaving depth, the greater the load variation range of the units, making it more difficult for flexible peak shaving units to complete peak shaving tasks within the required time. As a result, start-stop peak shaving units must respond to load demands by starting and stopping promptly. It can be observed from Figure 8 that the start-stop frequency is minimized when the ramp rate is between 2% and 3%, as the units can maintain both flexibility and reliability at this ramp rate. Moreover, before reaching a 50% peak shaving depth, the start-stop frequency is the lowest at a 4% ramp rate. At this point, the load adjustment range of the units is relatively small, and the 4% ramp rate enables the units to adjust flexibly within a certain range, thus reducing the frequency of starts and stops. Figure 6: Comparison of system LOLP under different peaking schemes. As illustrated in Figure 9, the generation cost of the system decreases with an increase in the peak shaving depth of the random units.