Abstract: The stronger reactive power support ability of synchronous regulator can effectively improve voltage stability of renewable power grid. However,the synchronous condenser may be out of step after loss of field caused by the excitation system fault in actual operation,which will affect the safe operation of the power grid. In order to study the operation ability of synchronous condenser after loss of field under the different voltage of renewable power grid,the time-step finite element model of 300 Mvar synchronous condenser is established and its operation characteristics are calculated under the loss of field caused by the open-circuit and short-circuit fault of field winding. The differences of synchronous condenser electrical quantities under different excitation winding after loss of field are compared and analyzed. On this basis,the operation characteristic of synchronous condenser after loss of field is studied under the different voltages of renewable power grid,and the variation law of synchronous condenser operation ability after loss of field along with the initial reactive power is revealed. The results show that the system voltage required to maintain synchronous operation is increased along with the increase of the initial reactive power of synchronous condenser.