| Loop closing operation in distribution network is a necessary step of power systems operation, but it will generate large loop current and surge current, which directly affects the network safety. It is necessary that the power flow calculation is done before closing loop operation to ensure the feeder current do not exceed the allowable capacity of the feeder and the circuit breaker.As the distribution dispatch center can hardly acquire the real-time data from the external network, one-boundary-node and two-boundary-node equivalent models of the closed loop distribution network are established by Ward and Ward/REI equivalent. The models can be solved through the state estimation without the real-time data of the external network, which enhances the calculation accuracy.Because there is no power measurement on feeder lines, in this paper, a simple and effective method is proposed to obtain a max closed-loop feeder current which can reflect the practical currents and ensure the distribution security. The feeder loads are centralized on the different begin or end of the corresponding feeders, then the max stable current can be gained by power flow calculation.A method to calculate the surge current based on Thevenin's equivalent is proposed in this paper. The equivalent electric potential and impedance are calculated accurately through network power flow calculation and node impedance matrix and the relationship for surge current and stable loop current is gained. Further more, the impact of surge current on other branches is studied using current distribution coefficient.In the end, according to the maximum allowable stable loop current and surge current of the loop network, the threshold of the voltage amplitude and phase angle difference is calculated.Actual examples and simulation results verify the correctness and validity of the proposed methods, which can provide effective decision-making supporting information for dispatchers.
|
PDF Full Text Request