DC Commutation Failure Analysis for the Sending-Side System Fault in Hybrid UHV Half-Wavelength and UHV DC Transmission System

Commutation failure (CF) caused by the failure which occurs on the sending side of the ultra-high voltage (UHV) half-wavelength AC (HWAC) transmission system is studied. Firstly, a hybrid UHV HWAC and UHV DC transmission system model is built, and the essence of CF is revealed regarding the influences of various factors on occurrence probability of CF. Then, the mechanism of CF of the UHV DC transmission system caused by the fault at the HWAC line in the hybrid system is explored. The steady-state operation characteristics are obtained through characteristic analysis according to the quasi-steady-state model of the HWAC line, and a three-phase short-circuit fault is assumed on the sending-side of a HWAC line and its voltage characteristics are deeply analyzed. In the actual power system, the specific situation of DC CF caused by the fault of the HWAC line is verified and analyzed based on a large quantity of transient stability calculations. Comparative analysis of the effects on UHV DC lines of the faults which occur on different locations of a HWAC line is presented. The conclusions can provide a useful reference and reliable technical support for the development of HWAC system and maintain power grid security and stability.