ABSTRACT
This chapter analyses the change of distance protection characteristics of AC line and converter station and its influence on distance protection. During the grid fault, the MMC-High Voltage Direct Current (HVDC) system exports various short-circuit currents to the AC system, which can be a threat to the correct operation of distance protection. The measured impedance variation of the MMC-HVDC distance protection in the AC side is also analyzed. The influence and interrelated factors of the MMC-HVDC system to distance protection are proposed. Digital simulation of PSCAD/EMTDC is done to verify the validity of the analysis. Distance protection is a commonly used principle, which is based on the distance between the fault points to the protection equipment to estimate the transmission line malfunction. For the impedance relay of quadrangle characteristic, after the converter station sends out certain reactive power, the resist-operation risk of the distance protection of the MMC AC side system is reduced.
