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This paper introduces a current differential protection scheme, appropriate for application in medium voltage active distribution systems, where it is desired to keep the greatest possible number of loads and DG units energized during a fault. Conventional two-terminal percentage current differential relays are used to form successive, time-current-coordinated, differential protection zones. Multiple time-delayed differential elements in each protection zone guarantee coordination with the zone's lateral protection devices, as well as between successive differential protection zones. Sensitive time-delayed differential elements protect against relatively high-resistance faults, while instantaneous differential elements minimize protection speed whenever possible. Additional emergency differential elements deal with post-fault topology changes and breaker failure conditions enhancing the overall scheme's performance. The proposed scheme is applied to a model of real medium voltage distribution system with distributed generation, considering a ring topology operation. A detailed simulation-based study proves the applicability and enhanced performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper presents a new method for locating faults in multi-terminal direct current (MTDC) networks incorporating hybrid transmission media, including segments of underground cables and overhead lines. The proposed traveling wave type method uses continuous wavelet transform applied to a series of line current measurements obtained from a network of distributed optical sensors. The technical feasibility of optically-based dc current measurement is evaluated through laboratory experiments using Fiber–Bragg Grating sensors and other commercially available equipment. Simulation-based analysis has been used to assess the proposed technique under a variety of fault types and locations within an MTDC network. The proposed fault location scheme has been found to successfully identify the faulted segment of the transmission media as well as accurately estimating the fault position within the faulted segment. Systematic evaluation of the method is presented considering a wide range of fault resistances, mother wavelets, scaling factors, and noisy inputs. Additionally, the principle of the proposed fault location scheme has been practically validated by applying a series of laboratory test sets. [ABSTRACT FROM AUTHOR]

This paper presents a method for rapid detection of faults on voltage source converter multiterminal HVdc transmission networks using multipoint optical current sensing. The proposed method uses differential protection as a guiding principle, and is implemented using current measurements obtained from the 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. [ABSTRACT FROM PUBLISHER]