A Novel Method for Seamless Closed-Loop Load Transfer in Radial Distribution Networks

Closed-loop load transfer is an effective measure to improve the power supply reliability of radial distribution networks. However, the traditional closed-loop load transfer mode is passive for operators: the loop closing operation relies on complex network models and calculation methods, which is feasible for the distribution network with many sensors, but it is not practical for the low-voltage distribution network with a complex structure. The field operation is still based on the experience of operators, resulting in uncertainty of the loop closing and large loop-closing current. Besides, the coordination of multiple power sources for guaranteeing power supply can not guarantee the power quality and the economic cost is high, in which the adopted closed-loop device is not movable and has poor reusability. This article presents an active loop-closing mode: a seamless closed-loop load transfer system (SLTS), which can not only realize uninterrupted load transfer but also eliminate loop closing surge current and expand the application range of closed-loop load transfer. In the proposed system configuration, a series compensation voltage source is connected to two substations. Therefore, closed-loop current can be controlled flexibly by regulating this voltage source. The proposed system can be applied to adjacent substations to carry out closed-loop load transfer operations during equipment maintenance. Besides, it can be installed between two radial feeders to achieve seamless fault seal-healing. The control strategy of seamless closed-loop load transfer and fault seamless self-healing are proposed, respectively. The effectiveness of the proposed SLTS and the designed control strategy are validated via MATLAB/Simulink.