## 7 Economic Analysis of D-FACTS Systems  
The global market for FACTS and D-FACTS systems is expected to reach $1,386,010,000 in 2018, it had already reached $912,850,000 in 2012 [12]. The D-SVC is the most widely used solution in the world market, followed by fixed capacitor banks. However, devices such as D-STATCOM are one  
Figure 17: Active power at the PCC during the voltage drop at the 60 kV bus. Figure 18: Reactive power at the PCC during the voltage drop at the 60 kV bus. customized solution for specific requirements of the distribution network. Obviously, some D-FACTSs are relatively expensive because they consist of many components such as advanced power electronics components, thyristors, reactors, capacitor banks, switches, protection systems and control systems. In this section, the range of the cost of the key features is often taken from the company Siemens and the Electric Power Research Institute (EPRI) with the database specified in [13], as shown in Figure 19.  
Generally, the cost of a D-FACTS system has two components: the installation costs and operating expenses. The total cost of the entire installed systems comprises the equipment price and the delivery and installation of these systems. The operating cost includes the cost of maintenance and service. Specifically, the operating cost of these devices is approximately 5% to 10% of the total installation cost. Therefore, the cost functions for the D-SVC and D-STATCOM are developed as follows [15]:  
\[\left\{ \begin{array}{l}C_{SVC}=0.0004\,s^{2}-0.262\,s+81.5\\ C_{SVC}=0.0003\,s^{2}-0.305\,s+127.38\\ C_{STATCOM}=0.0004\,s^{2}-0.3225\,s+128.75\\ C_{STATCOM}=-0.0008\,s^{2}-0.155\,s+120\end{array} \right. \tag{1}\]  
where \(s\) is the operating range of D-FACTS devices kVAr. The marginal cost per kVAr of the installed D-FACTS devices decreases as the operating rate of capacity increases. An overall cost for reactive power 100 MVAr, D-SVC ranges from $60 to $100 per kVAr. Although the D-SVC has sophisticated components such as thyristors, inductors and capacitors, it has a control structure that is relatively simple. Similarly, based on Figure 19, the overall cost of a D-STATCOM varies from $100 to $130 per kVAr and 100 MVAr of operating range. The costs of the installed parallel D-FACTS devices are shown in the Table 2[16]:  
From the above table, we see that the cost of D-FACTS devices (D-SVC and D-STATCOM) is much more expensive compared to capacitors due to the cost of the control devices and the complexity of the design and application of D-FACTS systems. The D-STATCOM is the source of reactive power \begin{table}
\begin{tabular}{c c} \hline \hline
**Parallel Reactive Compensator** & **Cost (US \$/kVar)** \\ \hline Shunt capacitor & 8/kVar \\ D-SVC & 60/kVar \\ D-STATCOM & 100/kVar \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Costs of different reactive power compensators. Figure 19: Cost of the operation range for different D-FACTS devices. Reproduced from [14]. compensation that is more expensive because of the used power electronics components like the Insolated Gate Bipolar Transistor (IGBT). In this study, the Figure 20 summarizes the performance of both D-FACTS types (D-STATCOM and D-SVC), also by comparing the amount of injected reactive power (MVAr) and the installation cost of these devices ($). This comparison provides a basis for system integration D-FACTS in a wind farm consisting of the DFIG type of generator helping to achieve a better balance between performance and cost in the condition of specific defects. The D-STATCOM provides a very effective reactive power compensation with respect to the D-SVC for all fault conditions. However, the D-SVC has a capacity option for a large amount of reactive power to be injected during a severe fault condition of the source. In the case of a two-phase ground fault (worst event of the grid fault applied in this study), the cost of installation is an important factor to consider.