Development And Research Of Closed-loop Current Analysis System For 10kV Distribution Networks

The closed-loop operation is an effective way to solve the problem when the equipment was repaired and the load was transferred in the distribution networks. However, the generated large closed-loop steady-state current would cause over-current protection movement, which would directly affect the power grid safety. The actual network before the closing loop operation can be simulated with the developed system in this paper, operator would combine the computation results with their operational experience to determine whether closed-loop operation should be done and transfer load based on the simulation and calculation of the loop current, so it has strong practical engineering value.In this paper, we put forward an equivalent model of 10kV distribution network closed loop current calculation which considers the phase angle changing of main transformers, the external network equivalent impedance can be calculated through utilizing method of geometric proportion, the steady-state current is obtained by adopting two-stage method. Based on the analysis of the transient process in time domain, the mathematic expression of the loop power flow was established and discussed, the main factors that determined the loop power flow were found. Two actual lines of Urumqi were carried on closed loop experiment, the simulation results verified the effectiveness of the loop current calculation and analysis, and analyzed the influence that the various variables bring about, including the phase angle changing of main transformers, the voltage proportional coefficient of main transformer and the variable line between main transformer and substation.We chose VB6.0 as the development tool to develop the closed loop current analysis system of distribution network, which would construct the number of components of power flow calculation required and develop modeling combined with the actual situation to distribution network of Urumqi, the system of visual power flow and graphical interface would be realized. We adopt SQL Server as the database management system to store and process data files, the calculation and analysis would go ahead through collecting the real-time monitoring data in distribution network from SCADA system. It is fast and accurate to aid operators to make the closed loop operation, which improves the reliability of closed loop operation in distribution network.