DC line protection for VSC-HVDC system

Voltage source converters based HVDC (VSC-HVDC) systems involving overhead transmission lines are prone to severe over-currents and over-voltages during dc line faults. This necessitates the operation of the system with some kind of protective devices to overcome the effects of dc line faults. Due to uneconomical and non availability of commercial DC circuit breakers the present day VSC-HVDC systems find applications only in back to back and/ or underground cable transmission, power ranging in the order of 400 MW. In the present work, the application of superconducting fault current limiter (SCFCL) along with chopper controlled resistors (CCR) is proposed to overcome the effect of over-voltages and over currents. The VSC-HVDC system is analysed with the high voltage and high current (110 kV, 2.8 kA) resistive SCFCL and the CCR in PSCAD/EMTDC environment. The results of analysis for various ac and dc fault conditions are quite encouraging.