Conventional overcurrent protection is hard to apply to modern distribution networks with high penetration of distributed generations and flexible operation modes. Current differential protection (CDP) is considered t...
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Conventional overcurrent protection is hard to apply to modern distribution networks with high penetration of distributed generations and flexible operation modes. Current differential protection (CDP) is considered to be a good solution, but the expensive cost of datasynchronization equipment limits its application. fault data self-synchronization (FDSS) methods realize the approximate datasynchronization according to the features of measured currents at both terminals, which makes it possible to achieve the low-cost CDP. However, the existing FDSS methods still have shortcomings such as low accuracy or complicated steps. In this paper, the principles and defects of existing FDSS methods are first analyzed, and then an improved FDSS method based on mathematical morphology (MM) is proposed. This method is realized by MM filter and MM-based peak-valley detection algorithm, which has higher synchronization accuracy and anti-noise ability. More importantly, in this method, the reference time required for synchronization can be obtained in the pre-communication process, which is easily implemented. The simulation based on PSCAD-MATLAB verifies the effectiveness of the proposed method under different fault conditions and its improvement compared with the existing method. Finally, the RTDS-based hardware test platform is used to verify the differential relay prototypes developed based on the proposed method.
The uncertainty in the direction and magnitude of fault current is a thorny issue for active distribution network (ADN) protection. Current differential protection (CDP) is suitable for ADN with complex operating mode...
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The uncertainty in the direction and magnitude of fault current is a thorny issue for active distribution network (ADN) protection. Current differential protection (CDP) is suitable for ADN with complex operating modes and multiple types of DGs. However, the datasynchronization conditions in transmission lines are usually not available in distribution systems with relatively low investment levels. fault data self-synchronization (FDSS) algorithm is a low-cost datasynchronization method specially used for the protection of distribution networks, but there will be large time synchronization errors under some extreme fault conditions. In this paper, the inherent defect of the conventional FDSS algorithm is first analyzed. Then an improved FDSS algorithm is proposed, which uses the current zero-crossing time and current slope polarity to estimate the starting delay difference at both terminals. On this basis, a corresponding CDP scheme is proposed. Compared with traditional CDP, the proposed scheme does not require additional synchronization equipment and high communication bandwidth. Finally, an ADN simulation model was built using PSCAD, and the improved FDSS algorithm program was implemented in MATLAB. Test results prove that the improved FDSS algorithm can effectively reduce the time synchronization error, and the corresponding CDP scheme is effective under various fault conditions.
To solve the impact of the integration of distributed generations on distribution network protection, current differential protection is introduced into the active distribution networks. Using faultdataself-synchron...
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To solve the impact of the integration of distributed generations on distribution network protection, current differential protection is introduced into the active distribution networks. Using fault data self-synchronization algorithm to construct current differential protection can reduce the cost of protection and communication, but the unsynchronized starting of relays on both sides will cause time synchronization errors and affect the reliability of protection, especially when high resistance faults occur at feeders with inverter-based DGs. In this paper, the cause of the starting delays of protective relays is analyzed through assumptions and approximations. On this basis, an adaptive current differential protection method for active distribution networks is proposed. This method uses the current amplitude ratio on both sides of the protected feeder to adaptively modify restraint current in differential protection, which can weaken the effect of time synchronization error caused by fault data self-synchronization algorithm and improve the performance of current differential protection. Finally, the effectiveness of the proposed method is verified in both PSCAD/EMTDC simulation and a closed-loop test platform based on the real-time digital simulator.
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