Virtual three-terminal current differential protection for distribution networks considering unmeasurable T-connected loads

Using current differential protection can solve the feeder protection issue caused by the connection of a high proportion of distributed generations to the distribution network. However, when there are unmeasurable T-connected load branches in the feeder, differential protection can only use the data from both terminals of the protected line to construct criteria. This affects its performance. To address this issue, the impact of unmeasurable T-connected loads on traditional two-terminal current differential protection is analyzed first, and then a virtual three-terminal current differential protection method is proposed. This method equates the unmeasurable T-connected branches inside the protected line to a virtual branch, estimates the current phasor of the virtual branch using voltage and current data at both terminals of the line before and after a fault, and finally forms a three-terminal current differential protection criterion together with the current phasors at both terminals of the feeder. The simulation results show that this method can meet the protection requirements of distribution networks in different scenarios without the need for T-connected load measurement data and has higher reliability and sensitivity than traditional current differential protection. © 2024 Power System Protection and Control Press. All rights reserved.