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Improving transient voltage stability is one of the most important issues that must be provided by doubly fed induction generator (DFIG)-based wind farms (WFs) according to the grid code requirement. This paper proposes adjusted DC-link chopper based passive voltage compensator and modified transient voltage controller (MTVC) based active voltage compensator for improving transient voltage stability. MTVC is a controller-based approach, in which by following a voltage dip (VD) condition, the voltage stability for the WF can be improved. In this approach, a voltage dip index (VDI) is proposed to activate/deactivate the control strategy, in which, two threshold values are used. In the active mode, the active and reactive power are changed to decrease the rotor current and boost the PCC voltage, respectively. Based on the control strategy, in a faulty grid, DFIG not only will be able to smooth DC-link voltage fluctuations and reduces rotor overcurrents but also it will increase the voltage of point of common coupling (PCC). Therefore, it improves transient voltage stability. The simulation results show the effectiveness of the proposed strategy for improving voltage stability in the DFIG. [ABSTRACT FROM AUTHOR]

Since the insulators of transmission lines are exposed to different environmental conditions, it is important task to study insulators performance under different conditions. In this paper, silicone rubber insulators performance under different environmental conditions including rainy, icy, salt and cement are proposed and exactly is studied. Electric fields (E-fields) and voltage distributions along the insulator under various conditions have been evaluated. Moreover, the corona rings effects on insulator performance under these conditions have been presented. A 230 kV silicone rubber insulator is selected, modeled and simulated with finite element method (FEM) using the COMSOL software. The simulation is repeated for different environmental conditions and efficiency of corona ring for each scenario is evaluated. The results indicate that environmental conditions have a significant effect on the insulator performance and the corona ring somewhat alleviate the adverse effect of environmental conditions on the insulator performance. [ABSTRACT FROM AUTHOR]