Study of Calculation Schemes of Currents Induced by Closing-Loop Operations in Medium-Voltage Distribution Grids

To avoid large currents caused by closing-loop operations in medium-voltage distribution grids, it is necessary to develop an effective method for rapid and accurate calculation of the closing-loop currents. In this paper, theoretical analysis is conducted to obtain the typical equivalent circuit for the calculation and analysis of the typical 10kV closing-loop system in Shanghai Grid. Three methods considering both the calculation complexity and the result accuracy, namely detailed power flow analysis method, simplified power flow analysis method and approximate formula method are proposed based on the typical equivalent closing-loop system. In the case study, the closing-loop currents of 10kV distribution grid of Shanghai under various operation scenarios are calculated with the three methods respectively, and the influence of the load levels and transformers’ tap positions on the closing-loop currents are analyzed in accordance with the practical requirements of dispatching. The validity of the three methods is confirmed through comparison of the calculation results with full-network simulation results through BPA software. Furthermore, the convergence, accuracy and practical applicability of the three methods are compared, thus to provide a feasible and reliable decision basis for practical distribution grids dispatching.