## 5 Operational Descriptions of the Future Distribution Networks with the Sundom Smart Grid
### Protection Use Cases of the Microgrid Phase  
In the microgrid phase, protection is considered for the MV and LV distribution networks, which both can form a microgrid. In this instance, the analogy of the microgrid area protection is intended for both voltage-level microgrids. In connection with the MMS, the MPMS is responsible for the microgrids' protection coordination. The protection system is adaptable depending on the microgrid's operation mode (grid-connected or island) and, if necessary, on the production and demand changes. The MPMS must react to various fault situations in both operation modes. The LV microgrids' protection system could be based on the combination of current and voltage measurement because the inverter-connected DG units can cause the short circuit current to be low and delay the operation of a protection device (PD). The LV feeder protection can be implemented by circuit breakers (CBs) with electronic trip units. The electronic trip units can measure voltage, current, and frequency on which the different protection functions are based. The protection functions can be against overcurrent (OC), directional OC, earth fault, phase unbalance, under/over frequency, under/over voltage, and power reversal. Timestamps of the event data are used to log the events in the correct sequence [96]. In this study, the operational scenarios are developed regarding OC protection. Figure 5 presents an exemplary outline of a microgrid in the Sundom smart grid area. The microgrid is considered to be formed within the MV distribution grid (or the LV distribution grid). There are PDs located in the MV or LV distribution networks. The numbering of the PDs carries the analogy of a microgrid. PD0 and PD1 are marked as (0) and (1) in the primary substation (and the secondary substation), whose function is to isolate the microgrid from the utility grid during the fault conditions in the supplying feeder (F1). The (1) includes the microgrid main switch, or it is connected to control the microgrid main switch. PD2s marked as (2) are for the MV (or LV) feeder line protection against the fault F2, and they are capable of performing adaptive protection functions based on a command from the MPMS to change their protection settings. The PD3 Cs marked as (3C) are for the LV feeder line protection against fault F3, and they are CB-based devices. The PD3 Fs \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt}} \hline \hline
**HL-UC Name** & **Events in the LV and MV Distribution Networks** \\ \hline \multirow{6}{*}{Control power flow at the POI} & MV: The secondary control regulates the voltage deviations of the WT, the CHP, and the PS-BESS. In addition, the OLTC can be connected to the power balancing in the grid-connected mode. For example, during the high generation and low consumption time, the voltage level can rise in the LV grids and highly cabled MV grid, in which case the PS-BESS (and SS-BESS) can be charged. \\ \hline \multirow{3}{*}{Control power flow at the POI} & LV: \\  & MV: The MEMS is in charge of the tertiary control in the grid-connected mode aiming to provide the setpoints for active and reactive power flows at the POI according to the microgrid’s operational target \\ \hline \multirow{3}{*}{Seamless switching between the operation modes} & LV: \\  & MV: The MEMS is responsible for synchronizing the different control loops, thus enabling smooth transitions between the different operation modes. The secondary controller includes the synchronization control loop for the switching between the islanded and grid-connected modes. \\ \hline \hline \end{tabular}
\end{table} 
Table 6: \(Cont.\)marked as (3F) are for customer installation protection, and they are traditional fuse-based devices. The PD4s marked as (4) are the protection devices for the DG units. The selectivity of the protection system in the MV (and LV) distribution network is established as follows [43; 96; 103; 104]:  
* The function of the PD0 is to isolate the substation from the utility grid during the line fault (F1) conditions.