The effects of TCPST on power frequency overvoltage in EHV line

As a new generation of flexible AC transmission devices, the Thyristor Controlled Phase Shifting Transformer (TCPST) has the function of controlling power flow distribution, restraining oscillation and improving system dynamic characteristics, and has a wide application prospect. At present, the TCPST is still in the theoretical research stage in China, and the influence of the TCPST on the overvoltage of power frequency should be considered to ensure a safe and stable operation of the system when making use of it. Based on the composite two-port theory, this paper combines the line distributed parameter model and the simplified TCPST model, and theoretically analyzes the influence of the TCPST and its impedance and phase shift on the line capacitance overvoltage, asymmetric fault overvoltage and load rejection overvoltage. Then, with reference to the parameters of the existing PST engineering project, the electromagnetic transient simulation analysis of power frequency overvoltage on the double circuit transmission line of the same tower is carried out to verify the correctness of the above theoretical inference. The results show that with the TCPST installed on the 500kV transmission line, the power frequency overvoltage caused by no-load capacitance effect rise and fault-free load rejection has an increasing trend, also the power frequency overvoltage caused by single-phase grounding fault has an inhibitory trend. However, the power frequency overvoltage caused by fault load rejection needs to be determined in combination with the actual situation and to be monitored carefully.