As a rotating equipment, the condenser can not only provide short-circuit capacity for the system, but also has good reactive power output characteristics. However, the longterm phase-leading operation of the condenser will affect the safety and stability of the condenser itself and the power grid. It is necessary to study the characteristics of the voltage regulation of the condenser in terms of reducing the transient over-voltage at the DC transmission end, dealing with the DC commutation failure, bipolar blocking and three-phase permanent fault of the AC system. Based on the analysis of the operation mechanism of the condenser and the case of the long-term leading-phase operation in ZLT, the operation status of the power grid near the ZLT converter station is simulated and analyzed by PSASP. The influence of different starting mode and DC power on the supporting ability of dynamic reactive power is calculated. The research shows that the operation mode of the condenser can meet the demand of system, which provides a theoretical support for the safety and stability of the system.