Abstract: For the power electronics dominated large power system, the risk of voltage recovery, even voltage instability, is becoming more and more serious. In this paper, a detailed dynamic simulation model which is described by a transfer function for a synchronous generator, an important reactive power source for voltage recovery, is presented. Secondly, the influence of the d-axis transient open-circuit time constant on the reactive power output of the generator and of the generator-capacitor combination is evaluated, and the evaluation indexes of reactive power support capability and voltage recovery performance are proposed. Thirdly, the countermeasures to mitigate the adverse effects of the sub-transient potential response delay and the capacitor output reduction due to voltage dropping are proposed. The effectiveness of the evaluation indexes and the countermeasures are verified by time-domain simulation of a large disturbance occurring in the Power Grid with UHVDC fed in Jiangxi province.