On dc faults in multi-terminals VSC-HVDC systems

Dc faults in multi-terminals High Voltage Direct Current (HVDC) Voltage Source Converter (VSC) systems are studied in this paper. The fault contributions of each component (coming from ac side or dc side) in the dc fault current are investigated through time simulations. Matlab simulation package is used in which an exciting two terminals HVDC-VSC model is extended to a 3 terminals HVDC-VSC model. The dc fault is occurred in the dc network connecting the three HVDC-VSC converters. Results of time simulations of dc fault current showed that the fault current experiences two main distinct periods; a decaying discharging current period fed by the energy storing elements in the dc side, and a delayed period of a fault current fed by the ac side. The first period is instantaneous and occurs just after the fault time and of very high peak current.