# Preliminary Design of the Electrical Power Systems for DTT Nuclear Fusion Plant
## 4 Operating Scenarios: Grid Calculations and Studies  
The outcomes of the electrical load analysis were used as the basis to obtain a preliminary design of the distribution system. Then, the electrical configuration was implemented in the DigSILENT PowerFactory software environment to be validated. PowerFactory is a power system software for the analyses and simulations of generation, transmission, distribution and industrial electrical power systems, covering the full range of models and functionalities [24, 25], from the traditional algorithms to real-time simulations. The same software was adopted for the preliminary design of the DEMO electrical power system [9, 16]. In the present paper PowerFactory was used to implement the power flow method [26] and the fault analysis to verify the correct design of the main electrical components. The assumptions used for the simulations are the following:  
* The steady state loads were accounted for at 100% (duty factor). * The pulsed loads were accounted for at 100% in the normal operating scenario. * The loads marked as intermittent were accounted for at 50%. * The loads marked as stand-by were accounted for at 10%. * Load power factors were assumed to be equal to those identified in the electrical load list. * Nodal voltage variations were accepted within \(\pm\)5% during operation and \(\pm\)10% in case of violation of the constraint. * The OLTCs were considered only for the 150/20 kV transformers supplying the SSED section. * The taps for the PPED transformers were kept fixed at a value that was identified as optimal. Such value may be adapted in no-load conditions in case of variations in the voltage from the external grid. A different strategy including OLTCs would make sense only for operations of some minutes [27]. * The earth resistance \(R_{\mathrm{e}}\) was assumed to be equal to 230 \(\Omega\) for the 150/20 kV transformers, while \(R_{\mathrm{e}}\) was equal to 100 \(\Omega\) for the 20/6.3 kV transformers. At the LV level, the transformers were directly connected to the ground (i.e., \(R_{\mathrm{e}}=0\)). Various operating scenarios were analyzed in order to cover the most significant operating conditions. In particular, the simulations were carried out by varying the configuration of the distribution system (the MV network in single or double radial configuration), connecting and disconnecting the power factor correction systems, under different load conditions. The two extreme instances that were studied are the maximum load scenario in a single radial network configuration and the no-load scenario in a double radial network configuration. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**PPED Section**} \\ \hline \multirow{2}{*}{**LC**} & \multicolumn{3}{c}{**Load Demand**} & \multicolumn{1}{c}{**Power Factor without**} \\ \cline{2-5}  & **MW** & **MVAr** & **MVA** & **Correction System** \\ \hline
1 & 21.7 & 22.9 & 31.6 & 0.69 \\
2 & 72.9 & 38.9 & 82.6 & 0.88 \\
3 & 0.0 & 0.0 & 0.0 & – \\
4 & 0.0 & 0.0 & 0.0 & – \\
5 & 106 & 34.9 & 112 & 0.95 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Active, reactive and apparent power required by DTT distribution LCs, PPED section. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{5}{c}{**Total Pulsed Load**} \\ \hline \multicolumn{1}{c}{**MW**} & **MVAr** & **MVA** & **PF** \\ \hline
201 & 96.8 & 223 & 0.90 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Total active, reactive and apparent power required by PPED distribution subsystem of DTT. To properly design and size the electrical distribution system, suitable network calculations and studies were performed:  
1. Power flow analysis, to verify the correctness of the sizing of each equipment and power line and to define some operating parameters, such as the optimum position of the taps of power transformers. Moreover, the power flow calculations allow to define and size the needs for power factor compensation systems. 2.