# A Study of Order Modification for Reactive Power Support by Wind Farm during Communication Failure
## 3 Case Studies  
### System Configuration  
To check the proposed algorithm and its related schemes, an EMTDC simulation was configured within a composed wind farm layout. A 7 MW/8 MVA full-converter-based wind turbine was utilized to compose a 350 MW wind farm system. The real power control processes were based on the WFMS, which utilized the curtailment option for matching imposed power demand. Figure 5 shows the entire layout, while Table 1 shows a basement system, including the main transmission line for the utility grid. The equivalent source of the entire power grid is incorporated by considering the short circuit ratio (SCR), which is used to estimate the robustness of the system. Further system configurations are equal to the previously analyzed wind farm layout (Table A1). The cable data set is utilized from the website of Reference [20], and the straight line distances for each array are described in Table A2.  
Table 2 describes the designed verification processes that analyze the response improvement of the proposed method. The simulation time is designed to be 4.75 s, which includes a short initialization time, and an order changed point for verification. To estimate the main improvements of the proposed reactive power control scheme, an initial stable wind speed is applied in order to calculate full-extraction conditions. The low voltage condition, and related reactive power order changes, are then gradually imposed on the WFMS, causing reactive power reference variations.  
Figure 4: Entire control flow chart, including newly imposed calculation.  
Figure 6 shows the verification concept. If the changed references at next sequence (the sequence interval was named as \(t_{order}\)) are not appropriately transferred to each wind turbine, in the case of the previous controller, the wind turbine controller refers to the previous reference, even if it involves TSO order variations. To check the order modification method, the communication error section is configured before the low voltage condition is induced as described in Table 3. The wind turbine trip condition is also considered, in the case of C. The tripped wind turbine is designated with consideration to the highest proportion of the reactive power in the array 1 (WT1). Additionally, array 5, which has the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Transmission System**} & \multicolumn{2}{c}{Cable Size} & C0 & \\  & \multicolumn{2}{c}{Cable length} & 20 (2 line) & Km \\ \hline \multirow{3}{*}{**Main Grid**} & SCR & 15 & \\  & X/R & 15 & \\  & Base voltage & 154 & kV \\ \hline \multirow{2}{*}{**Wind Farm Configuration**} & Connection height-C1 size & 149.7 & M \\  & Base voltage & 22.9 & kV \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic information for test system.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Simulation Time**} & Start-up & 0.75 & s \\  & \multicolumn{2}{c}{\(t_{order}\)} & 2 & s \\  & Total simulation time & 4.75 & s \\ \hline \multirow{2}{*}{**Utilized Wind Profile**} & 350 (full extraction) & MW \\ \hline \multirow{2}{*}{**Low Voltage Condition**} & Induced time & 2.75 & s \\  & Voltage level & 0.97 & p.u. \\ \hline \multirow{2}{*}{**Reactive Power Order Change (TSO)**} & First order & 50 & MVAR \\  & Second order & 100 & MVAR \\ \hline \hline \end{tabular}
\end{table}
Table 2: Imposed numerical value in basic case study.  
Figure 5: Wind farm configuration and related values.