Nonlinear Transient Mathematical Model of Large-Capacity Synchronous Condenser Based on Time-Varying Reactance Parameters

Large-capacity synchronous condenser (SC) is an essential dynamic reactive power compensation device in an Ultra-high voltage direct current (UHVDC) transmission system. The particular trans- ient operating state and structural characteristic of SC lead to a severe magnetic saturation effect during transient operation. To accurately describe the dynamic characteristics of SC, it is urgent to establish a transient mathematical model considering the magnetic saturation effect. Therefore, this paper proposes a nonlinear transient mathematical model for SC based on time-varying reactance parameters and gives a calculation method for time-varying reactance parameters. The mathematical model proposed in this paper is verified by taking a 300MVar SC as the research object. This condenser is connected to the power grid at the sending end of the UHVDC transmission system. The proposed mathematical model, the traditional fixed-parameter transient mathematical model, and the saturated standard SG model used in the power system were used to simulate the voltage generated by dynamic reactive power compensation characteristics of SC during a drop failure. Compared with the fault test results, the accuracy of the proposed mathematical model is verified. The effect of magnetic saturation on the dynamic reactive power compensation characteristics was analyzed, respectively. In addition, the accuracy of the proposed mathematical model is closer to the actual motor state, which is helpful for further research on the operation analysis and state monitoring of SC.