# CoSimulating Communication Networks and Electrical System for Performance Evaluation in Smart Grid
## 5 Simulation Study
### Simulation Results
Note that the \"pu\" means the fraction of actual voltage to defined base voltage. As the actual voltage gets closer to the base voltage (i.e., 1 pu), the system can be regarded as a more stable system. Table 2 describes the total power loss and the voltage index of the 13 Node system for 5 min. From the results we can note that through the DR application, the power loss can be reduced and the voltage stability of the distribution system can be maintained. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Total Power Loss** & **Voltage Index** \\ \hline w/o DR & 33,385 kW & 0.1533 \\ DR (Ideal) & 22,795 kW & 0.0741 \\ DR (WLAN Mesh) & 23,125 kW & 0.0783 \\ DR (WiMax-Ethernet) & 23,094 kW & 0.0825 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The power loss and the voltage of 13 Node system. Figure 10: The power consumption in 13 and 34 node systems. (**a**) 13 Node system; (**b**) 34 Node system. By observing the results, we can conclude that the designed DR application can successfully contribute to stable and efficient distribution system. A notable point of the simulation results of Figure 11a,b and Table 2 is that the impact of the underlying network infrastructure is relatively small. Since the 13 node system is very a small system, the performance gap between the two network systems is very small, and it causes little differences of the simulation results. We can note that both WLAN network and WiMAX network scenarios tend to converge to the ideal network scenario. However, when we conducted a simulation with 34 Node system, we can precisely see to what extent the network performance affects the distribution system. Because the 34 Node system is a much more large system than the 13 Node system, there exists much greater differences between the application performance of WLAN Mesh and WiMax-Ethernet backbone network. Figure 12a shows the total power loss that we simulated from the 34 Node system. Basically, the DR application also could achieve its goal in 34 Node system. However, there exists large difference between the WiMax-Ethernet backbone and WLAN Mesh network. Since the 34 node system consists of many energy management systems, the probability of packet collision was seriously increased. It led the performance degradation of the DR application. Moreover, a number of packets were dropped due to the multi-hop transmissions, which led the unexpected result. However, the WiMax-Ethernet backbone network shows almost similar performance to the ideal scenario. Figure 12b shows the voltage of the 852 bus in the 34 Node system. We can see that the energy management function can successfully maintain the distribution system stable. However, when we employed WLAN Mesh network, we cannot achieve grid stability since the network has poor connectivity and few energy management systems receive the control information in desirable time. Table 3 shows the total power loss and voltage index of the 34 node system. The application which employs WLAN Mesh network system shows larger power loss and higher voltage index value. Therefore, we can conclude that to employ WLAN based backbone for DR application in the 34 node system, a new protocol which can resolve the low connectivity issue should be designed. For example, modified MAC protocols or routing schemes, which can guarantee high delivery ratio in multi-hop wireless network, should be introduced to construct WLAN based backbone network. Figure 11: The power loss and the voltage of 13 Node system. (**a**) Total power loss; (**b**) Voltage of 652 bus. In addition, we analyzed the transmission delay of network packet in each scenario. The transmission delay of the smart grid network is one of the critical issue since an excessive delay of the power state report could lead to the delayed control of the power distribution, which results in the unexpected power loss. We ran the OOCoSim simulation for each scenario (13 and 34 node system and WLAN Mesh and WiMAX network system) for 600 s and collected packet response provided from the OPNET in each simulation.