Single-ended differential protection in MTDC networks using optical sensors

This paper presents a method for rapid detection of faults on VSC multi-terminal HVDC transmission networks using multi-point optical current sensing. The proposed method uses differential protection as a guiding principle, and is implemented using current measurements obtained from optical current sensors distributed along the transmission line. Performance is assessed through detailed transient simulation using Matlab/Simulink® models, integrating inductive DC-line terminations, detailed DC circuit breaker models and a network of fiber-optic current sensors. Moreover, the feasibility and required performance of optical-based measurements is validated through laboratory testing. Simulation results demonstrate that the proposed protection algorithm can effectively, and within very short period of time, discriminate between faults on the protected line (internal faults), and those occurring on adjacent lines or busbars (external faults). Hardware tests prove that the scheme can be achieved with the existing, available sensing technology.