Single terminal coordination-protection scheme for hybrid three-terminal DC line based on station terminal current characteristics

Abstract

Grounding electrode is an essential component in hybrid multi-terminal HVDC transmission system, By connecting converter station to the bus bar as a main station, this work analyzes the fault current component characteristics of grounding electrode line under various fault conditions for a hybrid three terminal DC transmission system. It is concluded that under single pole line grounding fault, current at the measuring ends of grounding, fault and sound electrodes satisfies the Kirchhoff current theorem, while considering converter station as a node. However, for reverse fault of line protection, current at above mentioned electrodes doesn’t follow the Kirchhoff law. Under various DC line faults, fault line is selected according to the mutation direction of current at the back-side of bus bar. Essentially, the current obtained by grounding electrode’s measuring point is a zero mode current, hence, it can sense the fault current precisely and has directivity. A comprehensive single terminal coordination-protection scheme for DC lines in hybrid multi-terminal transmission system is constructed by using currents’ characteristics of station terminal. The proposed method does not rely on boundary elements, and has an ability to quickly identify internal and external faults, select the fault pole, and withstand high resistance. The developed algorithm for protection scheme is simple, requires low sampling rate, and ensures high reliability for protection scheme.