# Power Quality Issues and Mitigation for Electric Grids with Wind Power Penetration
## 4 Simulation of Voltage Mitigation
### Results of Selected Case Studies
#### 4.3.1 Transmission System Case Studies  
The IEEE 30-node test network comprises of 30-node, 41-line, and 256.4 MW total base demand. The system has six generators that are connected at nodes \"1\", \"2\", \"5\", \"8\", \"11\", and \"13\". The complete circuit of the IEEE 30-node is shown in Figure 8 which is based on reference [56]. The WPP is connected at node \"30\" of the IEEE 30-node test system [57]. Three cases are analyzed that include: Case 1 the system without any wind penetration at node '30', Case 2 the capacity of the WPP is taken small as 10 MW, and finally Case 3 the capacity of WPP is 50 MW which is about penetration level of 25% of the total base demand. Figure 6: Normalized load profiles of a substation located in Riyadh city. Figure 7: Intermittent wind power generation profile. In all cases, the IEEE 30-node test system is analyzed using the FQSTS simulator at a loading factor of one and half of the base case demand for all simulations. The simulation is conducted based on a 1-s time step whereas the economic load dispatch is executed repeatedly every 15 min. During the 15-min timescale, load frequency control and base-point participation are regularly performed. Any deviation in the power balance within a timescale of 1-min is represented by a steady-state frequency drop which is corrected via base-point participation. The test shows the interaction features of various control actions in the study system during the simulation period of 24-h. As the FQSTS provides a grid simulation with many details for system variables, the focus of the analysis here is directed to the WPP reactive power compensation, and its impact on voltage mitigation. Case 1 System without wind penetration: the IEEE 30-node is analyzed without WPP at node \"30\". The voltage profiles of the voltage-controlled nodes and node \"30\" are exhibited in Figure 9. The results show that the available reactive power by synchronous machines is sufficient to keep the terminal voltage of the controlled nodes \"1\", \"2\", \"11\", and \"13\". The remaining generators at nodes \"5\" and \"8\" couldn't provide the necessary reactive power to keep the voltage at the desired reference value. This is mainly due to their excitation limits as well as high local reactive power demand and nodes \"5\" and \"8\". The voltage at node \"5\" becomes controllable again as the time approaches nontime. This is in line with demand variation in the kingdom of Saudi Arabia. According to the demand profiles shown in Figure 6, commercial demand drops, and residential demand increases during the nontime (12:00-4:00 PM). The generator at node \"5\" can provide 40 MVAR with a maximum local demand of 19 MVAR. Hence, the generator can control the terminal voltage if there is no high reactive power demand propagated from the network. However, this is not the case for the generator at node \"8\", the generator can only provide 10 MVAR whereas the maximum local demand is 30 MVAR which is much beyond the generator capacity even if there is a drop in the demand. Hence, the voltage \(V_{8}\) becomes uncontrolled as exhibited in Figure 9. Finally, the voltage \(V_{30}\) at node \"30\" which is a candidate location to install the WPP is uncontrollable since it is treated as a pure load node in the  
Figure 8: The IEEE-30 node standard test feeder with WPP at node ’30’ [56]. simulation. The results show that although node \"30\" has low active and reactive demand, the voltage drops beyond 95%. Case 2 System with 10 MW WPP: A 10 MW WPP is connected to the IEEE 30-node at node \"30\". The WPP is equipped with reactive power compensation facilities. Figure 10 shows that the voltage at the controlled voltage nodes and the voltage at the PCC of the WPP. Generators at nodes \"1\", \"2\", \"11\", and \"13\" have the necessary reactive power to keep the terminal voltage of these power plants at their desired reference value. However, the remaining generators have limited reactive power as discussed in Case 1.