The voltage security becomes more important to avoid voltage collapse, particularly, in N-1 criterion. Voltage Instability Proximity Index (VIPI) is used to assess the margin of voltage stability. At certain time interval, system load is often regarded as constant, and VIPI is computed. However, with the system penetrated wind farms (WFs) highly, the generation of WFs varies extremely from low generation to nominal generation following variation of wind speed. Thus, the margin of voltage stability varies with respect to the generation variation of WFs in a time. It is necessary to foresee the variation range of VIPI and voltage fluctuation from the stochastic perspective. Monte Carlo Simulation (MCS) is utilized to create samples of correlated WFs, and compute the VIPI corresponding to these examples. Based on the marginal distribution of VIPI and voltage, impact of WFs may be forecasted, and the probability of each value VIPI and voltage fluctuation is determined. In this study, we control static condensers with minimum capacity for reducing the probability of VIPI and voltage fluctuation, which exceed operation risk, to defined values